THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 


'OTOMETRY 
GIFT  OF 


Dr.  Hugh  V.   Brown 


SQUINT 


ITS     CAUSES,     PATHOLOGY,     AND 
TREATMENT 


SQUINT: 

ITS      CAUSES,      PATHOLOGY 
AND    TREATMENT 


BY 

CLAUD    WORTH,    F.R.C.S. 


PHILADELPHIA 
P.    BLAKISTON'S    SON    AND    CO. 

1012     WALNUT     STREET 
1906 


Add'l 
GIFT 


Re 

OPTOMETRY 
UBKA- 


CONTENTS. 


CHAPTER    I. 
Introduction page  i 

CHAPTER    II. 

BINOCULAR   VISION. 

Binocular  vision — Grades  of  binocular  vision — Tests 
for  binocular  vision — The  normal  development  of  the 
fusion  sense  in  infancy  ....  page  7 

CHAPTER    III. 

CONVERGENT   SQUINT. 

General  description  of  the  anomaly — Clinical  varie- 
ties— Suppression  of  the  vision  of  the  deviating  eye — 
Diplopia  artificially  produced — Nature  of  diplopia — 
The  amblyopia  of  convergent  squint — The  power  of 
central  fixation  in  the  deviating  eye — False  fixation — 
False  macula — Monocular  diplopia — Apparent  vertical 
deviation — True  vertical  deviation — Spurious  squint  of 
infants — Spontaneous  "  cure  "  of  squint — Course  of  an 
untreated  case  of  squint — Age  of  onset  of  squint — 
Refractive  error  in  convergent  squint — Statistical 
tables — Relative  frequency  of  squint     .         .        page  25 

CHAPTER  IV. 

THE   ^ETIOLOGY   OF   CONVERGENT   SQUINT. 

Muscle  theory — Donder's  theory — ^Etiology  of  con- 
vergent squint — Defect  of  the  fusion  sense  the  funda- 
mental cause — Subsidiary  causes — Proofs  of  the  Author's 
contention    .......        page  48 


292 


vi.  CONTENTS 

CHAPTER   V. 

AMBLYOPIA,    CONGENITAL   AND   ACQUIRED. 

Congenital  amblyopia  —  Acquired  amblyopia  — 
Illustrative  cases — Amblyopia  in  cases  of  convergent 
squint — Statistical  tables      ....        page  63 

CHAPTER   VI. 

THE    METHOD    OF   INVESTIGATING   A   CASE    OF    SQUINT. 

History— The  character  of  the  squint — Cover  test — 
Mirror  test — Diagnosis  between  squint  and  paralysis 
— The  power  of  central  fixation — The  movements  of 
each  eye  separately — Dynamic  convergence — Vision 
testing — Snellen's  types — The  ivory-ball  test — The 
examination  of  the  fusion  sense — Measurement  of  the 
angle  of  the  deviation — The  Deviometer — Maddox 
tangent  scale — Priestley  Smith's  tape — The  perimeter 
— Estimation  of  refractive  error  .         .        page  78 

CHAPTER    VII. 

THE   TREATMENT   OF   CONVERGENT   SQUINT. 

The  objects  of  treatment — The  means  by  which 
these  objects  may  be  attained — Optical  correction — 
Spectacles  for  children  and  for  infants— Occlusion  of 
the  fixing  eye— Instillation  of  atropine  into  the  fixing 
eye  only — Fusion  training — Operation — Indications  for, 
and  choice  of,  operation — Alternating  squints — Occa- 
sional squints— Vertical  deviations        .  .        page  97 

CHAPTER    VIII. 

THE   METHOD   OF   TRAINING   THE    FUSION   SENSE. 

Preliminary  remarks — The  age  at  which  the  fusion 
sense  may  be  educated — The  Amblyoscope— Its  illu- 
minating apparatus — Three  classes  of  object  slides — 
Fusion  training— The  method  of  overcoming  ^"sup- 
pression" Simultaneous  vision — Fusion  of  images — 
Increasing  the  amplitude  of  fusion        .  .      page  Il8 


CONTENTS  VII. 

CHAPTER  IX. 

DIVERGENT   SQUINT. 

Myopic  divergent  squint — Neuropathic  divergent 
squint — Non-comitant  divergent  squints  other  than 
paralytic — Divergence  in  extreme  myopia — Divergence 
of  blind  eyes — Divergence  secondary  to  tenotomy 

page  133 

CHAPTER  X. 

TREATMENT   OF   SQUINT. 
Illustrative  cases page  141 

CHAPTER  XI. 

HETEROPHORIA. 

Orthophoria — Heterophoria — Methods  of  testing 
the  muscular  balance  of  the  eyes — Esophoria  — 
Exophoria — Hyperphoria  —  Cyclophoria —  Illustrative 
cases page  164 

Insufficiency  of  dynamic  convergence      .      page  196 

CHAPTER  XII. 

OPERATIONS  ON  THE  EXTERNAL  OCULAR  MUSCLES. 

Advancement  of  a  rectus  muscle — The  author's 
advancement  operation — Musculo-capsular  advance- 
ment— -Secondary  advancements — Tenotomy — Com- 
plete central  tenotomy  ....     page  201 

APPENDIX. 

Details  of  cases  of  congenital  amblyopia— Prisms 
and  decentred  lenses — Results  of  fusion  training — 
Results  of  advancement  operations — Details  of  con- 
struction of  the  deviometer — Modifications  of  the 
amblyoscope — Advancement  forceps        .         page  210 

INDEX. 


PREFACE    TO    THE    FIRST    EDITION. 


By  examining-  a  very  large  number  of  cases 
of  squint,  and  watching  the  results  of  treatment 
during  a  number  of  years,  and  by  investigating 
the  visual  functions  of  normal-sighted  people, 
I  have  endeavoured  to  learn  the  causes  and 
pathology  of  squint.  The  methods  of  treatment 
which  I  employ  are  the  outcome  of  these 
observations. 

In  cases  of  constant  unilateral  convergent 
squint,  the  usual  routine  treatment,  by  glasses 
and  operation,  gives  extremely  unsatisfactory 
results.  In  about  one-third  of  these  cases,  the 
wearing  of  glasses  causes  the  eyes,  after  a  time, 
to  become  "straight."  In  the  other  two-thirds, 
the  deformity  may  be  more  or  less  removed  by 
operation.  But,  more  often  than  not,  the  deviat- 
ing eye  becomes  very  blind,  and  the  acquisition 
of  any  sort  of  binocular  vision  is  quite  the 
exception. 

On  the  other  hand,  cases  of  unilateral  squint 
in  which  treatment  is  commenced  early  and 
carried    out    by   the  methods  described   in    these 


pages  are  nearly  always  perfectly  cured,  having 
good  vision  in  each  eye,  and  good  binocular  vision. 

Since  1893  I  have  kept  detailed  notes  of  every 
case  of  squint  which  has  come  under  my  observa- 
tion. I  have  notes  of  2,337  squints  and  hetero- 
phorias.  Of  these  cases,  1,729  suffered  from 
convergent  squint.  The  cases  presented  them- 
selves in  the  out-patient  departments  of  the  West 
Ham  and  East  London  Hospital,  the  Lough- 
borough Hospital,  and  the  Royal  London 
Ophthalmic  Hospital  (Moorfields),  and  in  my 
private  practice. 

I  am  greatly  indebted  to  Mr.  Silcock  and 
Mr.  Holmes  Spicer  for  their  kindness  in  allowing 
me,  during  a  period  of  nearly  four  years,  to 
investigate  and  treat  the  cases  of  squint  attending 
their  out-patient  clinics  at  Moorfields. 

I  wish  to  thank  Mr.  R.  E.  Hanson  for  valuable 
assistance  in  working  out  the  statistics  of  my  cases. 

138,  Hurley  Street, 

London,   IT. 
May,  1903. 


PREFACE  TO  THE  SECOND  EDITION. 


I  take  this  opportunity  to  thank  my  confreres, 
both  at  home  and  abroad,  for  the  very  generous 
reception  accorded  to  the  work. 

In  preparing-  the  second  edition,  nothing  has 
been  altered  or  omitted.  But  some  small  addi- 
tions have  been  made,  and  some  matters  more 
fully  discussed. 

Dr.  E.  H.  Oppenheimer  has  translated  the 
book  into  German  (for  Messrs.  Julius  Springer 
and  Co.,  Berlin). 


PREFACE    TO    THE    THIRD    EDITION. 

The  third  edition  contains  statistics  which 
give  a  fair  idea  of  the  results  which  may  be 
expected  from  the  methods  of  advancement  and 
fusion  training  described  in  these  pages. 

May,  1906. 


SQUINT: 

Its  Causes,  Pathology   and  Treatment. 


CHAPTER    I. 

INTRODUCTION. 

This  chapter  contains  nothing  new.  It  deals 
very  briefly  with  certain  elementary  facts. 

EMMETROPIA  is  the  refractive  condition  of  the 
normal  adult  human  eye.  Rays  of  light  proceeding 
from  a  single  point  on  a  distant  object  may,  for 
practical  purposes,  be  regarded  as  parallel.  When 
these  parallel  rays  enter  an  emmetropic  eye,  they 
undergo  refraction  as  they  pass  through  the  refracting 
media  (cornea,  aqueous  humour,  lens,  vitreous  humour), 
and  are  brought  to  a  focus  on  the  retina.  Rays  from 
every  other  point  in  the  distant  object  are  similarly 
focussed,  so  that  a  complete  (inverted)  image  of  the 
object  is  formed  on  the  retina.  The  refraction  which 
takes  place  under  these  conditions  is  called  the  static 
refraction  of  the  eye. 

Accommodation. — Rays  of  light  which  enter  the 
eye  from  a  near  object,  e.g.,  a  printed  page,  are  sensibly 
divergent.  Now,  it  is  obvious  that  the  static  refrac- 
tion of  the  normal  eye,  which  exactly  suffices  to  bring 
parallel  rays  to  a  focus  on  the  retina,  will  not  accu- 
rately   focus    these    divergent    rays.      To    meet    this 


2  INTRODUCTION 

deficiency,  there  is  a  muscle  within  the  eyeball,  the 
ciliary  muscle,  which,  by  its  contraction,  causes  the 
lens  to  become  more  convex,  more  nearly  spherical, 
and  so  increases  its  refractive  power.  This  act  of 
increasing  the  refractive  power  of  the  eye  is  called 
accommodation,  and  the  additional  refraction  thus  pro- 
duced is  called  the  dynamic  refraction  of  the  eye. 

Presbyopia. — In  childhood  the  lens  is  very  soft 
and  elastic,  and  is  easily  made  to  change  its  shape 
under  the  action  of  the  ciliary  muscle,  so  that  children 
have  a  very  wide  range  of  accommodation.  As  age 
advances,  the  lens  gradually  becomes  more  and  more 
firm  and  incompressible,  so  that,  though  distant  objects 
are  still  perfectly  focussed  by  means  of  the  static 
refraction  of  the  eye,  the  increase  of  refraction,  pro- 
duced by  the  action  of  the  ciliary  muscle  on  the  lens, 
becomes,  after  a  time,  insufficient  for  the  focussing  of 
near  objects.  For  this  reason,  a  normal-sighted  person 
of  fifty  must  either  hold  his  book  at  a  greater  distance, 
in  order  that  the  rays  of  light  proceeding  therefrom 
shall  be  more  nearly  parallel,  or  he  must  supplement 
his  weakened  accommodation  with  a  pair  of  convex 
glasses. 

Atropine,  when  instilled  into  the  conjunctival  sac, 
has  the  property  of  temporarily  paralysing  the  ciliary 
muscle,  and  so  suspending  entirely  the  power  of 
accommodation.  An  atropised  normal  eye  sees  dis- 
tant objects  distinctly,  by  virtue  of  its  static  refraction, 
but  is  quite  unable  to  focus  the  divergent  rays  pro- 
ceeding from  a  near  object.  In  other  words,  atropine 
produces  an  artificial  presbyopia. 

FIXATION. —  In  the  centre  of  the  retina  is  the  macula 
Intra,  whieh,  in  the  human  eye,  is  far  more  sensitive 
to  ordinary  visual  impressions  than  any  other  part. 
It  is  desirable,  therefore,  that  the  eye  be  brought  into 
such   a    position    that    the    image   of    any    object    which 

especially  engages  our  attention  shall  be  formed  upon 

tin-   macula   lutea.      The   eye   is   then   said   to  "  fix  "  the 


INTRODUCTION  3 

object.  An  imaginary  line,  passing  from  the  centre 
of  the  macula,  through  the  optical  centre  of  the  eye,  to 
the  object  looked  at,  is  called  the  visual  axis. 

Convergence. — When  the  two  eyes  look  at  a  dis- 
tant object,  the  visual  axes  may,  for  practical  purposes, 
be  considered  to  be  parallel.  When,  however,  a  near 
object  is  looked  at,  the  two  eyes  must  rotate  inwards, 
in  order  that  both  visual  axes  may  be  directed  to  the 
same  object.  This  active  inward  rotation  of  the  eyes 
is  called  dynamic  convergence.  In  the  case  of  a  normal 
pair  of  eyes  there  is  no  such  thing  as  static  convergence, 
because  the  primary  position  of  the  visual  axes  is  one 
of  parallelism.  In  a  case  of  convergent  squint,  how- 
ever, there  is  a  static  convergence  corresponding  to  the 
angle  of  the  deviation. 

Accommodation  and  Convergence.  —  When  a 
person  with  a  normal  pair  of  emmetropic  eyes  looks 
at  a  near  object,  the  eyes  converge  in  order  that  both 
visual  axes  may  be  directed  to  the  object.  At  the 
same  time  each  eye  "accommodates,"  in  order  that  the 
rays  of  light  from  the  object  may  be  accurately 
focussed  on  its  retina.  These  two  functions,  ac- 
commodation and  convergence,  are,  in  ordinary 
life,  always  used  together,  so  that  they  have  become 
"  associated "  by  hereditary  and  individual  habit.  It 
is  difficult,  therefore,  for  a  normal  pair  of  eyes  to 
accommodate  without  converging  or  to  converge 
without  accommodating. 

Conjugate  Movements. — In  looking  to  the  right, 
or  left,  or  up,  or  down,  the  two  eyes  move  together 
through  exactly  the  same  angle. 

Movements  oe  each  Eye  Separately.  —  The 
extreme  range  of  upward  and  downward  rotations  of 
a  single  eye  varies  slightly  in  different  people,  the 
average  being  about  46°  up  and  56°  down.1     Outward 

1  These  figures  are  the  average  of  measurements  which 
I  made  on  64  normal-sighted  persons  with  Stephens' 
tropometer. 


4  INTRODUCTION 

rotation  (abversion)  may  be  considered  full  when  the 
edge  of  the  cornea  can  be  made  to  touch  the  outer 
canthus.  The  power  of  inward  rotation  (adversion) 
varies  considerably  in  different  people.  Most  people 
can  advert  each  eye  separately  through  an  arc  of  500. 
The  power  of  independent  adversion  tends  to  become 
less  as  age  advances. 

Hypermetropia. — For  purposes  of  discussion,  the 
refracting  media  of  the  eye  may  be  diagrammatically 
represented  as  a  simple  convex  lens.  In  the  emme- 
tropic eye,  as  already  explained,  the  strength  of  this 
lens  is  such  that  parallel  rays  of  light  are  brought  to  a 
focus  exactly  at  the  retina.  A  hypermetropic  eye  is 
shorter,  from  before  backwards,  than  the  emmetropic 
eye.  This  abnormal  shortness  causes  the  retina  to  be 
situated  too  near  this  diagrammatic  lens.  Now,  in 
order  that  parallel  rays  may  be  brought  to  a  focus  on 
this  abnormally  situated  retina,  the  focal  length  of  the 
diagrammatic  lens  must  be  shortened,  or,  in  other 
words,  the  strength  of  the  lens  must  be  increased. 
This  increase  in  strength  may  be  brought  about  either 
by  the  patient's  using  his  accommodation  in  distant 
vision  (and  still  more,  of  course,  in  near  vision)  or  by 
his  wearing  a  convex  spectacle  lens  in  front  of  the  eye. 
A  hypermetrope  may  be  able  easily  to  accommodate 
sufficiently  to  correct  his  refractive  error  in  distant 
vision,  but  may  have  difficulty  in  sustaining  the  addi- 
tional effort  of  accommodation  involved  in  looking  at 
a  near  object,  e.g.,  in  reading. 

Myopia  is  the  converse  of  hypermetropia.  A  myopic 
eye  is  abnormally  long  from  before  backwards,  so  that 
the  retina  is  at  a  greater  distance  from  the  centre  of 
our  diagrammatic  lens  than  is  the  case  in  the  em- 
metropic eye.  In  order,  therefore,  that  parallel  rays 
from  a  distant  object  shall  be  iocussed  on  the  abnor- 
mally situated  retina,  the  focal  length  of  the  diagram- 
matic lens  must  be  increased,  /.<•.,  the  strength  of  the 
lens  must  be  diminished.      The  only  way  in  which  this 


INTRODUCTION  S 

can  be  accomplished  is  by  putting  a  concave  spectacle 
lens  in  front  of  the  eye. 

If  an  indistinctly  seen  distant  object  be  gradually 
brought  nearer  a  myopic  eye,  the  rays  which  enter  the 
eye  therefrom  become  more  and  more  divergent,  till 
a  point  is  reached  at  which  the  static  refraction  of  the 
myopic  eye  is  just  sufficient  to  focus  these  divergent 
rays.  If  the  object  be  brought  still  nearer,  the  eye 
accommodates  and  so  still  sees  distinctly. 

Astigmatism. — In  the  human  eye,  the  greater  part 
of  the  refraction  takes  place  at  the  surface  of  the  cornea, 
where  the  rays  of  light  pass  from  the  air  into  the  much 
denser  medium,  the  corneal  substance.  The  normal 
human  cornea  is  approximately  a  segment  of  a  sphere. 
Sometimes,  however,  the  cornea  is  curved  more  in  one 
meridian  than  in  another,  so  that  it  is  slightly  oval — 
like  a  slice  from  the  side  of  a  cocoa-nut.  This  condi- 
tion is  called  astigmatism.  In  the  meridian  of  greater 
curvature  the  rays  will  be  refracted  more,  and  brought 
to  a  focus  sooner,  than  in  the  meridian  of  less  curva- 
ture. Consequently  the  picture  formed  on  the  retina 
will  be  blurred  and  indistinct.  In  order  to  equalise 
the  refraction  in  the  different  meridians,  a  cylindrical 
lens  must  be  used,  i.e.,  a  lens  which  is  curved  in  one 
direction  only. 

Anisometropia  is  an  inequality  in  the  static  refrac- 
tion of  the  two  eyes. 

Angle  Gamma.1 — The  visual  axis  does  not  exactly 
correspond  with  the  geometrical  antero-posterior  axis 

1  The  angle  gamma  which  I  have  described  is  the  angle 
which  is  measured  clinically  and  is  of  practical  importance. 
But,  since  the  visual  axis  need  not  necessarily  pass  through 
the  centre  of  motion  of  the  eye-ball,  mathematicians  have 
taken  as  one  of  the  boundaries  of  the  angle  gamma  a  line 
passing  through  the  centre  of  motion  of  the  eye-ball  to  the 
object  looked  at.  This  line  is  of  no  clinical  significance, 
as  its  direction  cannot  be  determined  except  on  paper. 
2 


6  INTRODUCTION 

of  the  eye-ball.  The  angle  between  the  visual  axis  and 
the  antero-posterior  axis  of  the  eye-ball  is  called  the 
angle  gamma.  Usually  the  visual  axis  passes  through 
the  pupil  to  the  nasal  side  of  its  centre.  Rarely  it 
passes  through  the  pupil  to  the  temporal  side  of  its 
centre,  in  which  case  the  angle  gamma  is  said  to  be 
negative. 

In  hypermetropic  eyes  the  angle  gamma  is  usually 
high,  so  that,  when  the  visual  axes  are  parallel,  the 
antero-posterior  axes  of  the  eye-balls  are  perceptibly 
divergent.  In  this  way  a  deceptive  appearance  of 
divergent  squint  may  be  produced  or  a  slight  con- 
vergent squint  may  be  masked. 

In  myopic  eyes  the  angle  gamma  usually  is  low  or 
even  negative.  In  the  latter  case,  while  the  visual  axes 
are  parallel,  the  antero-posterior  axes  of  the  eye-balls 
are  convergent,  so  that  convergent  squint  may  be 
simulated  or  a  slight  divergent  squint  masked. 


CHAPTER    II. 
BINOCULAR    VISION. 

When  the  eyes  are  in  the  primary  position 
(i.e.,  looking  straight  ahead  into  the  distance) 
the  fields  of  vision  of  the  two  eyes  overlap  every- 
where, except  in  a  sector  of  about  350  towards 
the  temporal  periphery  of  each  field.  In  other 
words,  everything  which  a  normal-sighted  person 
sees,  he  sees  with  both  eyes  simultaneously, 
except  objects  which  lie  on  his  extreme  right 
or  his  extreme  left.  These  are  seen  only  with 
one  eye. 

When  a  distant  object  engages  our  attention, 
the  two  eyes  are  brought  into  such  a  position 
that  a  picture  of  the  object  is  formed  simul- 
taneously on  the  central  part  of  each  retina. 
Similarly,  all  other  distant  objects,  within  the 
limits  of  overlapping  of  the  visual  fields,  are 
focussed  on  functionally  corresponding  parts  of 
each  retina.  The  impressions  thus  received 
from  the  two  eyes  are  blended  in  the  brain,  so 
that  we  are  conscious  only  of  one  single  picture. 
This  psychical  blending  of  the  two  sets  of  visual 
impressions  is  called  binocular  vision. 

The  binocular  vision  of  near  objects  is  a  more 


BINOCULAR    VISION 


*°s 


:    i 


Fig.  i. 


BINOCULAR    VISION  9 

complex  act,  inasmuch  as  the  brain  has  to  blend 
images  which,  for  the  most  part,  do  not  fall  upon 
geometrically  corresponding  points  of  the  two 
retinae. 

The  diagram  represents  a  pair  of  eyes  looking 
at  an  object  O  in  the  middle  distance.  An  image 
of  O  is  formed  on  the  macula  ML  and  MR  of 
each  retina.  Now,  it  is  obvious  that  only  objects 
lying  in  the  line  MR— O  (or  in  this  line  produced 
beyond  O)  can  be  focussed  on  the  macula  of  the 
right  eye.  Similarly,  only  objects  lying  in  the 
line  ML  — O  can  be  focussed  on  the  macula  of 
the  left  eye.  O2  is  an  object  lying  in  the  line 
MR — O.  An  image  of  O2  will  be  formed  on  the 
macula  of  the  right  eye.  But  the  image  of  O2 
formed  in  the  left  eye  will  not  be  on  the  corre- 
sponding point,  but  at  a  point  X,  considerably 
to  the  outer  side  of  the  macula. 

Take  a  practical  illustration  — look  steadily  at 
a  distant  object,  and  hold  a  finger  about  18  inches 
in  front  of  the  eyes.  The  finger  will  be  seen 
double,  the  left  image  corresponding  to  the  right 
eye,  and  the  right  image  to  the  left  eye  (crossed 
diplopia).  Now  look  at  the  finger,  and  the 
distant  object  will  appear  double,  the  diplopia 
this  time  being  homonymous. 

This  "physiological  diplopia"  must  be  con- 
stantly present,  in  looking  about  a  room  for 
example,  yet  we  are  not  ordinarily  conscious  of 
seeing  double.       This   customary   freedom   from 


IO  BINOCULAR    VISION 

diplopia  is  brought  about,  not  by  mental  sup- 
pression of  one  of  the  images,  but  by  the  mar- 
vellous elasticity  of  the  fusion  faculty.  Both 
sets  of  impressions  reach  the  brain,  and,  by  their 
combination,  assist  in  our  appreciation  of  the 
third  dimension. 

A  simple  experiment  will  demonstrate  the 
elasticity  of  fusion.  Place  in  the  amblyoscope 
(chapter  viii.)  the  slides  shown  in  fig.  13,  p.  124. 
The  two  slits  are  fused  into  one,  and  the  control 
marks  are  seen,  one  on  each  side.  Now  gradually 
diverge  the  tubes.  When  the  extreme  limit  of 
divergence  of  the  visual  axes  has  been  nearly 
reached,  fusion  of  the  slits  is  still  maintained,  but 
the  control  marks  recede  on  each  side  farther 
and  farther  from  them.  When  the  limit  is 
passed  and  fusion  can  no  longer  be  maintained, 
the  slits  suddenly  spring  apart.  As  each  slit  is 
on  the  same  slide  with  its  control  mark,  the 
distance  cannot  really  vary  ;  but,  within  certain 
limits,  the  mind  still  fuses  the  images  of  the  slits, 
even  when  they  no  longer  fall  upon  anatomically 
corresponding  points  of  each  retina.  This  experi- 
ment would  serve  as  a  proof,  were  any  needed, 
that  fusion  is  a  purely  psychical  process,  and  not 
merely  the  result  of  stimulation  of  corresponding 
sets  of  nerve  endings  in  each  retina. 

But  this  must  not  be  taken  to  indicate  that 
accurate  adjustment  of  the  relative  positions  of 
the  two  eyes  is  unnecessary.     The  law  governing 


BINOCULAR    VISION 


the  fusion  of  images  which  are  not  precisely 
similar  may  be  stated  as  follows  :  When  the 
images  formed  in  the  two  eyes  differ  in  shape, 
size,  or  position,  if  the  disparity  be  not  too  great, 
the  oculo-motor  apparatus  first  places  the  eyes 
in  the  most  favourable  relative  positions ;  the 
fusion  sense,  by  virtue  of  its  elasticity,  then  fills 
lip  any  gap  ivhich  may  remain. 

The  following  additional  experiments  were  suggested 
to  me  by  Dr.  Verhoeff,  of  Boston,  U.S.A. 


Fig. 


Fig.  3. 


Fig.  4. 


Fig.  5. 


Fig.  6. 


Place  fig.  2  and  fig.  3,  in  a  stereoscope.  The 
horizontal  lines  of  course  are  blended.  But  the 
oblique  lines  also  are  blended;  the  resulting  line 
appearing  perpendicular  to  the  horizontal  line.     This 


1  2  BINOCULAR    VISION 

blending  of  the  oblique  lines  cannot  be  accomplished 
by  any  rotation  of  the  eyeballs  round  a  fore  and  aft 
axis,  as,  in  this  case,  the  horizontal  lines  would  not  be 
blended. 

Again,  if  figs.  4  and  5  be  blended  in  a  stereoscope 
the  combined  image  resembles  fig.  6.  The  oblique 
lines  outside  the  circles  are  blended  into  a  perpendi- 
cular line,  but  the  part  within  the  circle,  which  is  seen 
with  one  eye  only,  retains  its  oblique  direction. 

In  a  case  in  which  each  eye  separately  has 
the  power  of  seeing,  but  in  which  binocular  vision 
is  absent,  one  of  two  conditions  must  be  present, 
either  (a)  the  mind  is  separately  conscious  of 
the  two  sets  of  impressions  received  from  the 
two  eyes  —  diplopia,  e.g.,  in  paralysis  of  an 
external  ocular  muscle  ;  or  (b)  the  mind  takes 
note  only  of  the  impressions  received  from  one 
eye  and  ignores  those  received  from  the  other 
— suppression,  e.g.,  in  an  ordinary  case  of  con- 
vergent squint. 

Grades  of  Binocular  Vision. 

Most  people  who  have  binocular  vision  have 
the  faculty  to  its  full  extent.  Anyone,  however, 
who  has  undertaken  the  orthoptic  training-  of  any 
considerable  number  of  squinters,  will  find  that 
those  who  see  binocularly  naturally  arrange  them- 
selves into  three  separate  and  distinct  classes, 
according  to  the  degree  in  which  they  possess 
the  faculty. 

These  may  be  called  :  — 


BINOCULAR    VISION  I  3 

First  Grade. — Simultaneous  macular  perception. 

Second  Grade. — True  fusion  with  some  ampli- 
tude. 

Third  Grade. — Sense  of  perspective. 

First  Grade.  Simultaneous  macular  percep- 
tion. —  A  patient  having  only  this  grade  of 
binocular  vision  sees  devices  in  a  stereoscope 
as  two  separate  pictures,  which  overlap  and  form 
one  only  when  they  are  put  in  certain  relative 
positions  corresponding  to  the  directions  indepen- 
dently assumed  by  the  visual  axes.  The  "  desire  " 
for  binocular  vision  is  absent,  so  that  no  effort 
will  be  made  to  maintain  fusion. 

Second  Grade.  True  fiision  with  some  ampli- 
tude. —  A  person  having  the  second  grade  of 
binocular  vision  not  only  fuses  the  retinal  images 
in  the  two  eyes,  but  can  make  some  effort  to 
maintain  fusion.  When  such  a  person  is  fusing 
the  pictures  in  a  stereoscope,  if  the  pictures  be 
separated  or  brought  together  the  eyes  will,  to 
a  certain  extent,  follow  them  in  the  interest  of 
binocular  vision. 

Third  Grade.  Sense  of  perspective. — The  two 
eyes  see  from  different  points  of  view.  In  looking 
at  any  solid  object,  such  as  a  pillar,  for  instance, 
the  right  eye  will  see  more  of  the  right  side  of 
the  object  and  the  left  eye  more  of  the  left  side. 
In  the  slightly  dissimilar  pictures  thus  focussed 
on  the  retinas  the  points  of  difference  are  not 
suppressed,    as  in  the  case  of  a   person    having 


14  BINOCULAR    VISION 

only  the  second  grade,  neither  is  the  observer 
conscious  of  diplopia.  The  psychical  blending  of 
the  two  slightly  dissimilar  sets  of  visual  impres- 
sions enables  him  to  appreciate  the  solidity  of 
surrounding  objects  and  assists  in  his  judgment 
of  their  relative  distances. 

There  is  a  wide  gap  between  grades  i  and  2. 
A  patient,  however,  who  has  grade  2  usually 
acquires  the  third  grade  also. 

Quite  as  important  as  the  grade  of  binocular 
vision  is  its  intensity.  A  person  whose  fusion 
sense  is  feebly  developed  may  possibly,  under 
favourable  conditions,  have  the  highest  grade 
of  binocular  vision.  But  the  intensity  of  his 
tendency  to  fusion  will  be  slight,  so  that,  under 
unfavourable  conditions,  he  easily  abandons  the 
effort  and  uses  one  eye  only.  One,  however, 
whose  fusion  sense  is  well  developed  will  have 
such  an  intense  tendency  to  binocular  vision  that 
nothing  will  make  him  abandon  it  while  both 
eyes  are  open.  (Except,  of  course,  a  muscular 
paralysis,  in  which  case  he  will  suffer  from 
persistent  and  intolerable  diplopia.) 

Tests  for  Binocular  Vision. 

Four  dot  test.  —  A  convenient  clinical  test, 
which  I  have  used  constantly  for  some  years, 
is  an  adaptation  of  Snellen's  coloured  glasses. 
For  want  of  a  better  name,  it  may  be  called 
the   "  Four  dot  test."     A   pure    red  glass  allows 


BINOCULAR    VISION 


only  the  red  rays  of  light  to  pass  through  it. 
A  pure  green  glass  transmits  only  the  green 
rays.      Therefore  light  which  has  passed  through 


Fig.  7- 

the  red  glass  cannot  be  seen  at  all  through  the 
green  glass,  and  vice  versa. 

A  piece  of  plain  ground  glass,  1 2  inches  by  9 
inches,  is  covered  on  the  back  with  opaque  black 
paper.  The  black  paper  has  four  round  holes  cut 
in  it,  each  3  inches  in  diameter,  as  shown  in  the 


I  6  BINOCULAR    VISION 

diagram.  The  lower  hole  is  left  clear.  Behind 
the  upper  hole  is  cemented  a  piece  of  red  glass. 
Behind  each  of  the  other  two  is  cemented  a  piece 
of  green  glass.  The  arrangement  is  mounted  in 
the  front  of  a  box  which  contains  an  electric  or 
other  bright  light. 

The  patient,  standing  five  or  six  yards  away, 
wears  a  trial  frame  with  a  red  glass  before  the 
right  eye  and  a  green  glass  before  the  left.  If 
now  he  sees  two  dots  (white  and  red)  he  is 
using  the  right  eye  only.  If  he  sees  three  dots 
(white  and  two  green)  he  is  using  the  left  eye 
only.  If  he  sees  four  dots  (white,  red,  and  two 
green)  he  uses  both  eyes,  and  has  at  least  grade 
i  binocular  vision.  If  he  sees  five  dots  (red, 
two  green,  and  the  white  seen  double)  he  has 
diplopia.  If  the  accuracy  of  the  patient's  answers 
be  doubted,  it  may  be  tested  by  changing  the 
glasses  in  the  spectacle  frame  from  one  eye  to 
the  other. 

The  amblyoscope  (see  chapter  viii.).  —  Adjust 
the  instrument  for  parallelism  of  the  visual  axes. 
Place  in  the  slots  the  slides  shown  in  fig,  13. 
If  the  patient  sees  the  two  slits  as  one,  and,  at 
the  same  time,  sees  both  the  dot  and  the  cross, 
he  has  grade  1  binocular  vision.  Now  diverge 
or  converge  the  tubes  of  the  instrument.  If  this 
can  be  done,  even  to  a  very  slight  extent,  while 
the  patient  still  fuses  the  slits  and  sees  both 
control  marks,  he  has  grade  2  binocular  vision. 


BINOCULAR    VISION  I  7 

For  children,  more  interesting  objects,  such 
as  figs.  1 6  and  17,  may  be  used  in  the  same 
way.  The  extent  to  which  the  tubes  may  be 
separated  or  brought  together  without  the  eyes 
becoming  dissociated,  may,  for  practical  pur- 
poses, be  taken  as  a  measure  of  the  degree  of 
development  of  the  fusion  faculty. 

Now  put  in  the  instrument  the  slides  shown 
in  fig.  18.  A  patient  with  grade  2  binocular 
vision  will  only  fuse  the  outer  circles  ;  but  he 
will  either  suppress  the  image  of  one  of  the 
inner  circles,  or  will  see  both  inner  circles  "  all 
mixed  up."  A  person,  however,  with  grade  3 
binocular  vision  sees  the  inner  circles  blended 
and  appearing  much  nearer  the  eye,  giving  the 
whole  device  the  appearance  of  a  tub  or  bucket 
bottom  up.  If  the  slides  be  now  changed  from 
one  tube  to  the  other,  the  inner  circle  will  seem 
farther  away,  as  if  he  were  looking  at  the  inside 
of  the  tub.  This  appearance  is  so  vivid  that 
even  young  children  can  tell  at  once  whether 
they  are  looking  at  the  outside  or  the  inside  of 
the  tub.  By  changing  the  slides  from  one  tube 
to  the  other  two  or  three  times,  guessing  on 
the  part  of  the  patient  is  rendered  impossible. 
I  know  no  better  test  for  the  "  sense  of  per- 
spective." 

Herings  drop  test  for  the  sense  of  perspective. 
— I  do  not  now  use  this  test  clinically.  The 
experiment  is,  however,  very  instructive. 


I  8  BINOCULAR    VISION 

The  test  apparatus  (fig.  8)  consists  of  a  shallow 
box  (of  about  the  size  and  shape  of  a  box  for 
twenty- five  large  cigars),  open  at  both  ends. 
From  one  end  two  arms  project.  The  extremi- 
ties of  these  two  arms  are  joined  by  a  fine  thread, 
on  the  middle  of  which  is  a  round  bead. 


Fig. 


The  patient  holds  the  open  end  of  the  box 
close  to  his  eyes,  and  looks  through  the  box, 
at  the  bead.  The  surgeon  now  drops  small 
objects  of  various  sizes,  such  as  cowrie  shells, 
sometimes  on  one  side  of  the  thread,  some- 
times on  the  other.  The  patient  is  asked  to 
say  whether  each  shell,  as  it  drops,  falls  on  the 
near  side  or  the  far  side  of  the  thread. 


BINOCULAR    VISION  I  9 

If  he  has  the  third  grade  of  binocular  vision, 
"  the  sense  of  perspective,"  he  will  almost  always 
answer  correctly.  If  he  has  not,  his  answers 
will  be  mere  guesses,  and  he  will  be  nearly  as 
often  wrong  as  right. 

The  principle  of  the  test  is  as  follows  : — The 
box  cuts  off  all  view  of  surrounding  objects, 
including  the  hands  of  the  surgeon.  The  size 
of  the  falling  objects  varies,  so  that  their  appa- 
rent size  gives  no  information  as  to  their  distance. 
The  view  of  the  falling  object  is  too  brief  to 
admit  of  any  movement  of  accommodation  or 
convergence,  or  any  lateral  movement  of  the 
patient's  head.  The  patient  is  thus  deprived 
of  all  auxiliary  means  of  judging  distances,  and 
has  to  depend  upon  his  "sense  of  perspective" 
alone. 

This  test  is  not  infallible.  I  once  made  the  dis- 
covery that  a  boy,  aged  n,  with  a  manifest  squint 
of  1 30,  could  tell  on  which  side  the  shell  fell,  almost 
every  time,  when  both  eyes  were  open.  When,  how- 
ever, I  covered  the  deviating  eye  his  answers  were 
as  often  wrong  as  right.  He  had,  in  the  deviating 
eye,  &  vision.  There  was  no  "  false  macula."  He 
had  no  diplopia  spontaneously,  but  it  was  easily  elicited 
with  a  candle  and  coloured  glasses.  I  have  since  met 
with  other  similar  cases.  The  explanation  is  probably 
this  : — In  trying  the  test  with  a  normal  pair  of  eyes, 
the  view  of  the  falling  shell  is  so  brief  that  there  is  no 
time  for  the  eyes  "  to  fix  "  the  shell,  so  the  images  of 
the  object  do  not  fall  upon  corresponding  parts  of  the 
two  retinae.  It  is  not,  therefore,  really  a  test  for  the 
sense   of   perspective    in    direct  vision,  but  a  test  for 


20  BINOCULAR    VISION 

the  subconscious    perception    of    "  physiological    dip- 
lopia "  in  more  or  less  eccentric  parts  of  the  retinae. 

In  none  of  these  cases  was  the  suppression  of  the 
vision  of  the  deviating  eye  very  profound,  so  that  a 
moving  object  would  probably  be  perceived.  As 
strictly  corresponding  points  are  not  required  in  this 
test,  it  seems  not  unlikely  that  the  mind  may  derive 
some  information  from  the  false  image',  by  making 
allowance  for  the  faulty  position  of  the  deviating  eye. 
This  is  not  difficult  to  believe  when  we  remember 
that,  in  a  case  of  squint  in  which  diplopia  has  been 
artificially  elicited,  the  angle  of  the  diplopia  is  often 
very  much  smaller  than  that  of  the  squint  ;  show- 
ing that  the  mind  ordinarily  makes  some  allowance 
for  the  position  of  the  squinting  eye. 

The  Normal  Development  of  the  Fusion 
Sense. 

In  two  large  creches  I  made  experiments, 
extending  over  nearly  a  year,  with  the  object 
of  gaining  some  knowledge  of  this  subject.  It 
would  be  tedious  to  describe  in  detail  the 
methods  employed.  I  therefore  give  a  general 
summary  of  results. 

From  the  earliest  infancy  the  pupillary  light 
reflex  and  the  fixation  reflex  are  present,  showing 
that  some  degree  of  vision  of  each  eye,  and  the 
preponderance  of  the  macula  region,  are  innate. 
If,  in  a  darkened  room,  the  light  of  a  candle  be 
suddenly  thrown  from  an  ophthalmoscope  mirror 
into  an  eye  of  an  infant  only  a  few  hours  old, 
the  eye  will  immediately  fix  the  mirror.  This 
fixation   is   purely  reflex  and    is  only  maintained 


BINOCULAR    VISION  2  1 

for  an  instant.  During  the  first  few  days  of  life 
the  infant  cannot  fix  a  steady  light,  but,  by 
suddenly  flashing  the  light  into  the  eye,  this 
reflex  fixation  may  be  repeatedly  obtained. 

At  the  end  of  two  or  three  weeks  most  infants 
will  fix  the  mirror  steadily  for  several  seconds 
at  a  time  with  one  or  other  eye,  but  will  not 
converge  both  visual  axes  accurately  in  looking 
at  a  near  object. 

At  the  age  of  five  or  six  weeks,  as  a  rule,  the 
positions  of  the  reflections  of  the  mirror  on  the 
child's  corneae  are  symmetrical,  showing  that 
the  child  is  fixing  the  mirror  binocularly.  But, 
now  and  then,  one  eye  turns  a  little  inwards,  or 
more  rarely  outwards,  while  the  other  fixes  the 
mirror. 

During  the  first  few  months  of  life  the  move- 
ments of  the  eyes  are  uncertain,  not  completely 
controlled  by  the  higher  centres  of  the  brain. 
The  eyes  move  more  or  less  together,  but  the 
slightest  gastric  or  other  disturbance  often  causes 
one  or  other  eye  to  deviate.  But  it  will  be 
noticed  that  this  want  of  coordination  is  confined 
to  movements  in  the  horizontal  plane.  The 
conjugation  of  the  two  eyes  for  vertical  move- 
ments is  well-developed  from  the  earliest  infancy  : 
one  does  not  see  one  eye  turn  up  or  down 
without  the  other. 

We  can  scarcely  suppose   that  any  degree  of 
binocular  vision  can  be  present  at  a  time  when 
3 


22  BINOCULAR    VISION 

the  coordination  of  the  eyes  in  horizontal  move- 
ments is  in  this  rudimentary  condition. 

A  little  later,  at  the  age  of  five  or  six  months, 
if  the  child's  attention  be  engaged  by  some  new 
and  bright  object  of  absorbing  interest,  such  as 
a  cut  glass  decanter  -  stopper  revolved  before 
a  candle  flame,  it  will  often  be  possible  for  the 
person  nursing  the  child  to  slip  a  large  prism 
before  one  of  his  eyes  without  his  appearing 
to  notice  it.  A  prism  displaces  the  image  of  an 
object  towards  its  apex.  Therefore,  if  binocular 
vision  is  to  be  maintained,  the  eye  must  also 
rotate  in  the  direction  of  the  apex  of  the  prism. 
If  a  prism  of,  say,  12°  has  been  successfully 
slipped  before  one  of  the  child's  eyes,  with  the 
apex  towards  the  nose,  the  eye  will,  in  many 
cases,  make  a  slight  inward  rotation,  showing 
that  the  child  has  some  sort  of  binocular 
vision.  In  some  cases,  however,  while  the 
naked  eye  continues  to  be  steadily  directed 
towards  the  object,  the  eye  behind  the  prism 
makes  no  inward  rotation.  The  vision  of  this 
eye  is  probably  suppressed.  These  resemble 
certain  cases  of  occasional  squint,  in  which 
binocular  vision  is  present  when  the  eyes  are 
"straight,"  but  suppression  of  the  vision  of  the 
deviating  eye  takes  place  when  the  squint  is 
manifest. 

After  the  end  of  the  first  year,  a  child  who 
allows    one    to    make    the    experiment    with    the 


BINOCULAR    VISION  23 

prism    apex    inwards    will    almost    always    turn 
in  the  eye  in  order  to  blend  the  images. 

When  the  experiment  is  tried  with  the  prism 
apex  up  or  down,  it  is,  of  course,  not  possible  for 
the  eye  to  make  an  independent  vertical  move- 
ment in  order  to  blend  the  images.  I  tried  this 
vertical  prism  with  some  of  the  more  tractable 
infants,  aged  twelve  to  eighteen  months,  who  had 
readily  made  the  compensating  inward  movement 
when  tried  with  the  prism  apex  in.  Some  of  them 
showed  their  disapproval  of  the  vertical  prism 
by  screwing  up  the  eyes  and  twisting  the  head. 
Others  made  up-and-down  conjugate  movements 
of  both  eyes,  sometimes  directing  their  attention 
to  the  upper  image  and  sometimes  to  the  lower. 

To  recapitulate  —  The  vision  of  each  eye 
separately,  the  preponderance  of  the  macular 
reo-ion,  and  the  conjugation  of  the  two  eyes  in 
vertical  movements,  the  human  infant  has  fairly 
well  developed  at  birth.  The  conjugation  of 
the  eyes  for  horizontal  movements  (intended  to 
subserve  the  function  of  binocular  vision)  is 
perfected  within  the  first  few  months  of  life. 
Between  five  and  six  months  one  finds  the  first 
certain  evidence  of  a  "  desire  for  binocular 
vision,"  though  probably  a  certain  degree  of 
binocular  vision  is  present  at  a  much  earlier 
period.  At  first,  if  any  obstacle  be  interposed, 
it  is  a  question  whether  an  effort  shall  be  made 
to  overcome  it,  or  whether  the  newly  acquired  art 


24  BINOCULAR    VISION 

shall  be  abandoned  and  the  vision  of  one  eye 
temporarily  suppressed.  Towards  the  end  of  the 
first  year  the  eyes  will  make  a  considerable  effort 
in  the  interests  of  binocular  vision.  If  the 
obstacle  prove  insuperable  the  child  suffers  from 
diplopia,  being  no  longer  able  to  suppress  the 
vision  of  one  eye. 

The  results  of  fusion  training  in  the  case  of 
squinters  would  seem  to  show  that  the  fusion 
faculty  normally  reaches  its  full  development 
before  the  end  of  the  sixth  year. 


25 


CHAPTER  III. 
CONVERGENT  SQUINT. 

In  most  of  the  text-books  squint  is  defined 
somewhat  as  follows  :  "  Squint  consists  in  a 
deviation  of  the  visual  axis  of  one  of  the  eyes 
from  the  correct  position  of  fixation."  The 
authors  have  mistaken  a  single  symptom  for  the 
whole  disease.  One  might  as  well  describe  Pott's 
disease  as  "a  deviation  of  the  spine  from  its 
normal  shape." 

Two  essential  conditions  are  present  in  every 
case  of  comitant  convergent  squint. 

(i)  An  abnormal  convergence  of  the  visual 
axes. 

(2)  A  defect  of  the  fusion  faculty. 
Other  conditions  may  also  be  found  : — 

(3)  The  vision  of  the  eye  which  is  not  being 
used  for  fixation  is  almost  invariably  suppressed. 

(4)  There  is,  in  rather  rare  instances,  more  or 
less  congenital  amblyopia. 

(5)  There  is  very  often  acquired  amblyopia  in 
the  deviating  eye,  as  the  result  of  neglect  or 
inefficient  treatment. 

(6)  There    is    usually  a  refractive  error,   com- 


26  CONVERGENT    SQUINT 

monly  hypermetropia  and  hypermetropic  astig- 
matism. 

J\In  a  healthy  person,  with  a  normal  fusion 
faculty,  the  "  desire  for  binocular  vision  "  causes 
the  two  eyes  to  be  directed  steadily  to  the  same 
object.  But  when  the  "  desire  for  binocular 
vision  "  is  absent  there  is  no  special  reason  for 
this  perfect  accord  between  the  movements  of  the 
two  eyes,  so  that  any  slight  cause  may  then  upset 
the  equilibrium  of  the  convergence  centre,  and  so 
cause  the  visual  axes  to  assume  permanently 
faulty  relative  directions  (see  chapter  iv.). 

Then,  when  the  patient  is  looking  at  a  distant 
object,  instead  of  the  visual  axes  being  parallel 
they  are  convergent.  But,  in  order  to  see  the 
object  distinctly,  the  patient  must  look  directly  at 
it  with  one  or  other  eye.  He  will  naturally 
choose  the  eye  which  has  the  smaller  refractive 
error.  He  cannot  overcome  the  abnormal  con- 
vergence, neither  can  he  move  one  eye  without 
the  other.  He  therefore  makes  a  conjugate 
lateral  movement  of  both  eyes  until  he  has 
brought  the  better  eye  into  the  required  position, 
the  other  eye  turning  still  more  in  towards  the 
nose.  So  that  the  better  eye  becomes  "  straight," 
and  the  worse  eye  manifests  the  convergence  of 
both.  The  eye  which  is  used  for  vision  is  called 
the  fixing  eye  ;  the  other  eye  is  called  the 
squinting  or  deviating  eye. 

If  a  patient  fixes,  say,  with  the  right  eye  and 


CONVERGENT    SQUINT  2J 

turns  in  the  left,  he  is  said  to  have  convergent 
squint  of  the  left  eye.  This  is  a  useful  conven- 
tion, but  it  must  be  remembered  that  it  does  not 
accurately  describe  the  condition,  as,  of  course, 
convergent  squint  really  concerns  both  eyes  and 
certain  cerebral  functions  as  well. 
Sin  a  case  of  convergent  squint  the  separate 
movements  of  each  eye  are  perfect.  When  one 
eye  is  covered,  the  other  eye  can  move  upwards 
(superversion),  downwards  (subversion),  inwards 
(adversion),  and  nearly  always  outwards1  (ab- 
version)  to  the  normal  extent. 

The  conjugate  movements  of  the  two  eyes  are 
perfect.  When  the  fixing  eye  moves  in  any 
direction,  the  deviating  eye  also  moves  through 
exactly  the  same  angle.  When  the  (previously) 
fixing  eye  is  screened,  and  the  patient  fixes  with 
the  (previously)  squinting  eye,  the  screened  eye 
manifests  a  deviation  exactly  equal  to  that  for- 
merly exhibited  by  the  other  eye.'2  In  other 
words,   the  squint  is  comitant. 

The  association  between  accommodation   (dy- 

1  In  1,523  cases  of  convergent  squint,  in  which  I  noted 
the  power  of  abversion  of  each  eye  separately,  I  found 
it  perfect  in  81  per  cent.  The  remaining  19  per  cent., 
in  which  abversion  was  deficient,  were  almost  all  cases 
of  long  standing.  The  defect  of  abversion  was  less  un- 
common the  longer  the  duration  of  the  deviation. 

2  In  a  case  of  uncorrected  anisometropia  the  patient  may 
accommodate  to  a  different  degree,  according  to  the  eye  he 
uses.  This  may  make  the  squint  appear  to  be  not  strictly 
comitant. 


28  CONVERGENT    SQUINT 

namic  refraction)  and  dynamic  convergence  is 
perfect.  When  the  fixing  eye,  after  looking  at 
a  distant  object,  suddenly  accommodates  for  a 
near  object,  the  squinting  eye  rolls  still  further 
inwards,  a  dynamic  convergence  being  super- 
added to  the  abnormal  static  convergence.  This 
dynamic  convergence  is  proportionate  to  the 
extra  effort  of  accommodation  involved  in  looking 
at  the  near  object. 

In  fact,  there  is  no  motor  defect  of  any  kind 
in  a  typical  case  of  convergent  squint,  but  the 
primary  position  from  which  these  movements 
start  is  a  "cross-eyed"  position  instead  of 
parallelism  of  the  visual  axes. 

Convergent  squint  presents  certain  clinical 
varieties.     These  may  be  classified  as  follows  : — 

(i)  Occasional  squint,  of  which  there  are  two 
classes :  (a)  Premonitory  occasional.  (6)  True 
occasional. 

(2)  Constant  unilateral  squint. 

(3)  Alternating  squint,  of  which  there  are  two 
distinct  classes  :  (a)  Accidentally  alternating- 
squint.     (6)  Essentially  alternating  squint. 

( 1 )  Occasional  squint. — A  patient  is  said  to 
have  an  occasional  squint  if  the  eyes  are  only 
occasionally  seen  to  deviate  from  their  normal 
relative  directions.  When  no  deviation  is  present, 
the  patient  usually  has  the  first  grade  of  binocular 
vision.  When  he  squints  he,  in  the  majority  of 
cases,  has  no  diplopia.     The  deviation  of  an  occa- 


CONVERGENT    SQUINT  2Q. 

sional  squint  is  in  some  cases  only  seen  for  a  few 
seconds  in  the  day,  in  others  the  eyes  are  almost 
as  often  "crossed"  as  not.  The  deviation  in 
different  cases  may  manifest  itself  under  various 
conditions,  e.g.,  in  near  vision,  on  looking  down, 
under  the  influence  of  any  strong  emotion  such 
as  fear  or  anger,  when  the  patient  is  tired,  &c. 
Most  frequently  no  immediate  exciting  cause  can 
be  assigned.  Occasional  squints  are  sometimes 
called  periodic.  I  have  notes  of  a  few  cases 
which  may  properly  be  called  periodic  squints, 
in  which  the  deviation  has  appeared  every 
alternate  day  as  regularly  as   a  tertian  ague. 

(a)  Premonitory  occasional  squints  are  simply 
the  precursors  of  constant  squints.  They  usually 
become  constant  after  about  two  or  three  months. 

(b)  True  occasional  squints  are  much  less 
common  than  the  premonitory  variety.  A  true 
occasional  squint  may  gradually  cease  to  show 
itself  as  the  fusion  sense  develops,  or  perhaps 
optical  correction  of  any  refractive  error  may 
relieve  the  condition,  or  it  may  maintain  its 
character  unchanged  throughout  life.  Many  of 
these  last  are  not  squints  at  all,  in  the  strict  sense 
of  the  word,  but  are  examples  of  esophoria,  the 
pathology  and  treatment  of  which  are  described 
in  chapter  xi. 

(2)  In  a  case  of  constant  unilateral  squint  the 
deviation  is  constantly  present,  though  the  angle 
may  vary  ;    and   it   is   always  manifested  by  the 


30  CONVERGENT    SQUINT 

same  eye,  when  both  eyes  are  uncovered.  When 
the  "  fixing  eye  "  is  screened,  it  turns  in  towards 
the  nose,  and  the  "squinting  eye,"  instead,  is 
directed  to  the  object  which  engages  the  atten- 
tion (unless  this  eye  has  lost  the  power  of  central 
fixation).  When  the  screen  is  removed,  the  fixing 
eye  immediately  recovers  itself,  and  the  squinting- 
eye  again  turns  in. 

(3)  Alternating  squint.  — When  a  squinter  fixes 
with  either  eye  indifferently,  without  covering  the 
other,  the  squint  is  said  to  alternate.  Of  all  con- 
stant squints,  about  85  per  cent,  are  unilateral 
and  15  per  cent,  are  alternating.  These  alterna- 
ting cases  arrange  themselves  into  two  distinct 
classes — (a)  Squints  which  accidentally  alternate, 
because  the  refraction  is  about  the  same  in  each 
eye,  do  not  essentially  differ  from  unilateral 
squints.  In  fact,  if  these  cases  are  untreated, 
usually  one  eye  gradually  comes  to  be  used  ex- 
clusively for  fixation,  and  the  squint  becomes 
unilateral. 

[p)  In  a  case  of  essentially  alternating  squint 
there  is  usually  little  or  no  refractive  error,  and 
the  visual  acuity  of  each  eye  separately  is,  as 
a  rule,  perfect.  But  these  patients  have  a  con- 
genital total  inability  to  acquire  fusion.  Alter- 
nating squinters  suffer  much  less  than  unilateral 
squinters  from  neglect,  because  each  eye  is  used 
in  turn,  so  that  the  vision  does  not  deteriorate. 
If  the    wearing    of  glasses    does    not    cause  the 


CONVERGENT    SQUINT  3  [ 

abnormal  convergence  to  disappear  (it  seldom 
does),  an  accurately  performed  operation  will 
remove  the  deformity.  But  the  total  absence 
of  the  fusion  sense  renders  a  perfect  cure  of  an 
essentially  alternating  squint  impossible. 

Suppression  of  the  vision  of  the  deviating  eye. — 
In  a  case  of  convergent  squint,  as  the  two  eyes 
are  not  directed  towards  the  same  object,  it  might 
be  thought  that  everything  would  be  seen  double. 
This  is  not  so,  however,  save  in  the  exceptional 
instances  referred  to  below.  The  visual  acuity 
of  the  deviating  eye  may  be  perfect,  but  the 
picture  formed  in  this  eye  is  mentally  ignored  or 
"  suppressed,"  the  attention  being  directed  solely 
to  that  formed  in  the  fixing  eye.  This  "sup- 
pression "  is  not  a  voluntary  act.  The  inability 
to  receive  impressions  from  both  eyes  simul- 
taneously is  due  to  the  defect  of  the  fusion 
faculty,  which  was  the  essential  factor  in.  allow- 
ing the  squint  to  occur  in  the  first  instance. 

This  suppression,  however,  does  not  always 
extend  over  the  whole  field  of  vision  of  the 
squinting  eye.  If  the  deviation  is  of  only  slight 
degree,  there  is  a  small  part  of  the  temporal  side 
of  the  field  of  vision  of  the  squinting  eye  which 
lies  beyond  the  limit  of  the  field  of  the  fixing 
eye.  In  this  small  area  moving  objects  are 
perceived  by  the  squinting  eye,  but,  as  a  rule, 
are  not  accurately  located.  Thus,  in  an  old  case 
of  convergent  squint,  in  which  the  deviating  eye 


32  CONVERGENT    SQUINT 

has  lost  the.  power  of  central  fixation,  the  extreme 
nasal  side  of  the  retina  of  this  eye  (corresponding 
to  the  extreme  temporal  side  of  its  field  of  vision) 
is  the  only  part  which  is  ever  exercised.  For 
this  reason,  if  the  fixing  eye  in  such  a  case  be 
covered,  and  the  patient  be  told  to  look  at  a  light 
with  the  deviating  eye,  this  eye  will  be  seen  to 
roll  still  further  inwards,  in  order  to  receive  the 
image  of  the  light  on  the  nasal  side  of  the 
periphery  of  the  retina. 

Occasionally  one  meets  with  a  squinter  who 
has  diplopia  of  a  faint,  unobtrusive  kind.  Squin- 
ters  never  complain  of  diplopia  as  a  trouble,  but 
one  now  and  then  meets  with  a  child  who,  on 
being  carefully  questioned,  admits  seeing  a  second 
image.  If  the  white  handle  of  an  ophthalmoscope 
be  held  up,  such  a  child  will  point  to  the  real 
handle  and  also  to  "the  sham  one,"  showing  that 
he  really  has  a  faint  homonymous  diplopia, 
though,  in  the  great  majority  of  cases,  he  has 
never  mentioned  it  before.  In  such  a  case  he 
evidently  has  some  trace  of  a  fusion  faculty,  but 
not  sufficiently  well  developed  to  prevent  the 
occurrence  of  a  deviation. 

Diplopia  artificially  produced.  —  In  a  case  of 
unilateral  or  accidentally  alternating  squint,  if 
the  deviating  eye  be  not  too  blind,  diplopia  may 
usually  be  induced  by  artificial  means.  For 
instance,  let  the  patient's  attention  be  directed 
to   a  candle   flame.      Place   in   a  spectacle    frame 


CONVERGENT    SQUINT  $$ 

a  red  glass  before  one  eye  and  a  green  glass 
before  the  other.  The  images  of  the  candle 
flame,  formed  in  the  two  eyes,  being  thus  dif- 
ferently coloured,  the  patient  is  often  enabled  to 
perceive  them  both  simultaneously. 

Nature  of  diplopia. — The  popular  idea  is  that 
a  squinter  sees  the  object  which  lies  in  the  axis 
of  the  deviating  eye  as  well  as  that  which  lies  in 
the  axis  of  the  "straight"  eye,  so  that  he  can 
keep  an  eye  on  two  places  at  once.  Even  in 
the  case  of  the  very  few  squinters  who  are  able 
to  see  double  spontaneously,  or  of  those  who  are 
enabled  to  do  so  by  artificial  means,  this  view  is 
not  correct.  A  squinter  who  suffers  from  diplopia 
sees,  with  his  deviating  eye,  a  faint,  eccentrically- 
placed  image  of  the  object  to  which  the  fixing 
eye  is  directed,  and  suppresses  the  image  of  the 
object  which  lies  in  the  axis  of  the  deviating 
leye.  In  other  words,  he  does  not  see  two  different 
[objects,  but  sees  two  images  of  the  same  object. 

The  direction  in  space  in  which  this  second 
image  is  mentally  projected  is  peculiar. 

Now,  in  a  case  of  paralysis  of,  say,  the  right 
external  rectus  muscle,  if  the  right  eye  deviates 
inwards  to  the  extent  of  200,  everything  seen 
with  this  eye  will  appear  to  be  exactly  200  more 
to  the  right  than  it  really  is  ;  in  other  words, 
there  is  homonymous  diplopia  of  200.  If  an  eye 
turns  out  to  the  extent  of  200  owing  to  paralysis, 
there  is   crossed   diplopia  of    exactly   200.       The 


34  CONVERGENT    SQUINT 

mind  entirely  ignores  the  faulty  position  of  the 
eye,  and  projects  everything  rigidly  as  though 
the  eye  were  straight.  In  a  case  of  convergent 
squint,  on  the  other  hand,  if  there  is  diplopia  this 
does  not  necessarily  correspond  in  degree  with 
the  angle  of  the  deviation  of  the  eye.  The 
eccentrically-formed  image  is,  in  any  case,  very 
faint.  Even  the  most  intelligent  patient  usually 
is  unable  to  describe  its  position  exactly,  as  the 
angle  of  the  diplopia  seems  to  vary  without  any 
corresponding  variation  in  the  angle  of  the  squint. 
In  most  cases  the  false  image  is  placed  about 
half-way  between  the  true  position  of  the  object 
and  the  position  which  would  correspond  to  the 
angle  of  the  squint.  It  would  seem  as  though 
the  mind,  being  informed  by  the  straight  eye  of 
the  true  position  of  the  object,  were  continually 
trying  to  reconcile  this  knowledge  with  the 
impressions  produced  by  the  eccentrically-placed 
false  image. 

The  amblyopia  of  convergent  squint. — When  a 
patient  first  comes  under  observation  after  having 
suffered  from  unilateral  squint  for  a  considerable 
time,  one  usually  finds  that  the  deviating  eye 
is  more  or  less  blind,  so  blind  sometimes  that 
fingers  can  scarcely  be  counted  close  to  the  face. 
This  amblyopia  is  sometimes,  to  a  certain  extent, 
congenital.  But  by  far  the  greater  part  of  it  is 
due  to  a  gradual  loss  of  function  in  an  eye  which 
is  never   used.      It   might  have  been  prevented. 


CONVERGENT    SQUINT  35 

This  is  plainly  seen  by  comparing  the  vision  in 
my  cases  which  came  under  treatment  soon  after 
the  first  appearance  of  the  squint,  with  the  vision 
in  the  cases  which  I  saw  for  the  first  time  only 
after  years  of  neglect  or  inefficient  treatment  (see 
pages  76  and  Jj). 

The  power  of  central  fixation  in  the  deviating 
eye. — In  a  case  of  unilateral  convergent  squint, 
if  the  fixing  eye  be  covered  the  vision  of  the 
(previously)  deviating  eye  temporarily  ceases  to 
be  suppressed.  In  a  fairly  recent  case,  this  eye 
is  then  directed  so  as  to  receive,  upon  its  macula 
lutea,  the  image  of  the  object  looked  at.  But  if 
the  case  be  long  neglected,  this  sensitive  central 
region  of  the  retina  suffers  much  more  from 
disuse  than  the  paracentral  zone,  while  the  peri- 
pheral region  suffers  very  little,  if  at  all.  As  the 
blindness  progresses  in  this  disused  eye,  a  stage 
is  at  length  reached  when  the  visual  acuity  of  the 
central  region  falls  below  that  of  the  paracentral 
zone,  and  later,  even  below  that  of  the  periphery 
of  the  retina.  If  the  fixing  eye  be  now  covered, 
the  deviating  eye  is  not  directed  so  as  to  receive 
upon  its  macula  the  image  of  the  object  which 
engages  the  attention,  because  the  macula  has 
ceased  to  be  the  most  sensitive  part  of  the  retina. 
This  eye  then  wanders,  without  remaining  steadily 
in  any  definite  position  (lost  fixation).  Or  it  may 
fix  with  some  part  of  the  paracentral  region,  or 
roll    still    further  in    towards    the  nose  so  as  to 


36  CONVERGENT    SQUINT 

present  the  extreme  nasal  periphery  of  the  retina 
for  the  purpose  {false  fixation). 

False  macula.  —False  fixation  is,  unfortunately, 
exceedingly  common  in  neglected  cases  of  uni- 
lateral squint.  But  the  variety  known  as  false 
macula  is  rare.  In  an  old  case  of  squint,  in  which 
the  angle  of  the  deviation  has  remained  exactly 
the  same  for  several  years,  and  in  which  the  sup- 
pression of  the  vision  of  the  deviating  eye  is  not 
profound,  the  mind  sometimes  learns  to  make  full 
allowance  for  the  faulty  position  of  this  eye.  So 
that  the  eccentric  image,  formed  in  the  deviating 
eye,  is  mentally  projected  to  the  same  spot  as 
the  true  macular  image,  formed  in  the  normally- 
directed  eye,  and  is  blended  with  it.  This  false 
macula  is  merely  a  small  area  which  has  escaped 
the  loss  of  function  which  has  overtaken  the  sur- 
rounding part  of  the  retina.  The  visual  acuity 
of  a  false  macula  is  never  greater  than  the 
normal  visual  acuity  of  the  region  in  which  it 
is  situated.  I  have  rarely  found  it  equal  to  ,.'■,  ; 
never  greater.  Many  of  these  patients  can  pass 
Hering's  drop  test.  If  an  eye,  with  false  macula 
in  a  position  of  convergence,  be  put  "  straight  " 
by  operation,  crossed  diplopia  is  produced.  This 
usually  passes  off  within  a  few  days,  but  occa- 
sionally it  persists  for  many  months. 

Monocula  diplopia. — In  an  eye  with  "  false 
macula,"  central  fixation  has  nearly  always  been 
lost.       Occasionally  it    is    preserved.      In  such  a 


CONVERGENT    SQUINT  T>7 

case,  if  the  fixing  eye  be  covered,  the  deviating 
eye  will  immediately  take  up  central  fixation. 
The  "  false  macula"  is  then,  as  a  rule,  suppressed. 
If  it  is  not,  the  result  is  monocular  diplopia.  This 
condition  is  exceedingly  rare.  In  my  detailed 
notes  of  more  than  two  thousand  cases  of  squint 
of  all  kinds,  I  find  monocular  diplopia  only  men- 
tioned four  times,  although  I  have  been  constantly 
looking  out  for  this  anomaly. 

Apparent  vertical  deviation. — On  applying  the 
mirror  test  in  a  case  of  convergent  squint,  one 
not  infrequently  notices  a  slight  upward  deviation 
also  :  then,  on  covering  the  originally  fixing  eye, 
and  causing  the  originally  deviating  eye  to  fix, 
one  sees  that  the  originally  fixing  eye  also  turns 
up  as  well  as  in.  If  the  wearing  of  glasses  causes 
the  convergence  to  diminish,  the  vertical  devia- 
tion will  also  diminish  proportionately.  In  the 
great  majority  of  cases  the  vertical  deviation 
increases  when  the  gaze  is  directed  towards  the 
side  of  the  fixing  eye  and  diminishes  or  disap- 
pears when  the  gaze  is  directed  away  from  the 
side  of  the  fixing  eye. 

In  some  cases  of  divergent  squint,  the  diver- 
gent eye  turns  a  little  down  also,  no  matter  which 
eye  may  be  fixing. 

A  possible  explanation  is  that  in  these  cases  the 
planes  of  adversion  and  abversion  of  the  two  eyes, 
instead  of  being  horizontal,  are  titled  down  and  out 
towards  each  temple.     Then,  when  the  fixing  eye  is 

4 


38  CONVERGENT    SQUINT 

moved  horizontally,  the  deviating  eye,  in  making  a 
corresponding  conjugate  movement  uncontrolled  by 
the  fusion  sense,  moves  in  this  titled  plane.  Take,  for 
example,  a  case  of  convergent  squint  200,  exhibiting 
this  double  upward  deviation.  Really  each  eye  is  con- 
vergent io°,  but  the  eyes  have  made  a  conjugate  move- 
ment of  io°  towards  the  side  of  the  fixing  eye  so  as  to 
bring  this  eye  "  straight  "  and  double  the  apparent 
convergence  of  the  deviating  eye.  The  fixing  eye  has 
thus  travelled  out  and  down  in  its  plane,  and  the 
deviating  eye  has  travelled  in  and  up.  A  further  conju- 
gate movement  towards  the  side  of  the  fixing  eye  will 
increase  the  difference  in  vertical  height.  A  conjugate 
movement  away  from  the  side  of  the  fixing  eye,  by 
bringing  the  eyes  to  corresponding  points  in  their 
respective  planes  of  rotation,  will  cause  the  vertical 
difference  to  lessen  or  disappear. 

True  vertical  deviation. — In  some  cases  of 
squint  there  is  a  true  vertical  deviation,  one  eye 
turning  up  when  it  becomes  the  deviating  eye, 
and  the  other  eye  turning  down  when  it,  in  turn, 
is  made  to  deviate. 

Spurious  squint  of  infants. — During  the  first 
few  months  of  life,  before  the  fusion  faculty  has 
made  much  progress  in  development,  it  frequently 
happens  that  the  eyes  converge  for  a  few  seconds 
or  a  minute  at  a  time,  in  response  to  some  gastric 
or  other  disturbance,  Or,  as  nurses  are  wont  to 
express  it,  "  Babies  squint  when  they  have  the 
wind."  This  is  of  no  importance.  Sometimes, 
too,  a  child,  whose  fusion  faculty  is  developing 
quite  normally  in  other  respects,  acquires  this 
faculty  rather  later  than  usual,  just  as  a  perfectly 


CONVERGENT    SQUINT  39 

healthy,  intelligent  child  may  be  late  in  learning 
to  talk.  One  may  then  see  one  or  other  eye 
turn  in,  occasionally,  for  a  minute  or  two  at  a 
time,  even  when  the  child  is  old  enough  to  walk. 
Later,  if  the  fusion  faculty  developes  normally,  it 
will  so  control  the  movements  of  the  eyes  as  to 
prevent  any  recurrence  of  the  deviation. 

But  if  the  child  "crosses  his  eyes"  for  many 
minutes  at  a  time,  or  if  one  eye  converges  while 
the  other  steadily  fixes  some  object,  or,  more 
especially,  if  the  deviation  is  always  manifested  by 
the  same  eye,  the  case  is  probably  one  of  true 
squint  and  demands  investigation  without  delay. 
And,  under  any  circumstances,  it  is  safer  to 
investigate  any  case  in  which  a  child  is  seen  to 
cross  his  eyes  occasionally,  rather  than  wait  until 
what  may  have  been  a  premonitory  occasional 
squint  becomes  a  constant  squint. 

"  Growing  out  of  a  squint!' — With  the  advent 
of  puberty,  the  angle  of  a  convergent  squint  often 
tends  to  become  somewhat  less  without  any  treat- 
ment. In  rather  rare  instances  the  eyes  become 
straight,  or  nearly  so,  and  the  patient  is  said  to 
have  "grown  out  of  the  squint."  But,  in  the 
case  of  a  unilateral  squint,  the  squinting  eye  has 
nearly  always  by  this  time  become  very  blind 
from  disuse. 

The  belief  in  the  spontaneous  cure  of  squint  is 
very  wide-spread  among  the  general  public.  This 
may  be  due  partly  to  the  fact  that  the  deformity 


40  CONVERGENT    SQUINT 

of  squint  does,  in  a  few  cases,  disappear  spontane- 
ously as  just  mentioned,  and  partly  to  the  fact 
that  an  occasional  squint  is  seen  at  one  time  and 
not  at  another,  but  chiefly,  I  think,  to  the  fact 
that  the  spurious  squint  of  infants  ceases  to 
manifest  itself  when  the  fusion  sense  developes. 

But,  unfortunately,  this  superstition  is  not 
entirely  confined  to  the  laity.  I  have  often  had 
a  child  brought  to  me  with  the  squinting  eye 
nearly  blind  from  neglect,  and  have  been  told 
that  the  family  practitioner  was  consulted  about 
it  years  ago  and  that  he  advised  the  parents  to 
"  wait  to  see  if  the  child  would  grow  out  of  the 
squint." 

General  course  of  an  untreated  case  of  constant 
unilateral  convergent  squint.  —  At  the  first  ap- 
pearance of  a  deviation,  the  squinting  eye  always 
has  the  power  of  central  fixation  when  the  fixing 
eye  is  covered,  and  the  vision  is  nearly  always 
good  in  both  eyes.  There  is  rarely  some  con- 
genital amblyopia.  This  congenital  amblyopia 
is  far  less  frequent  than  is  generally  supposed, 
and  is  never  responsible  for  the  extreme  blindness 
so  often  found  in  old  neglected  cases  of  squint. 

In  an  untreated  case,  the  vision  of  the  deviating 
eye,  being  entirely  suppressed,  gradually  deterio- 
rates from  disuse,  until,  in  many  cases,  central 
fixation  is  lost,  and  the  vision  reduced  to  the 
counting  of  fingers  close  to  the  face.  The 
younger    the    child    the    more    readily   does    this 


CONVERGENT    SQUINT  4  I 

amblyopia  from  disuse  occur.  So  much  so  that 
it  is  commonly  believed,  even  by  ophthalmic 
surgeons,  that  an  eye  which  begins  to  squint  in 
early  infancy  is  necessarily  very  blind,  and  this 
blindness  is  supposed  to  be  congenital.  Yet  this 
is  not  the  case.  Of  the  cases  which  came  under 
my  care  soon  after  the  first  appearance  of  the 
deviation  I  do  not  find  the  young  squinters 
especially  amblyopic  (see  chapter  v.). 

The  deviation,  in  an  untreated  case  of  con- 
vergent squint,  usually  increases  in  degree  up 
to  the  time  of  puberty.  After  this  time  it  often 
tends  to  become  gradually  less,  until  about  forty 
years  of  age,  when  in  some  cases  it  is  scarcely 
noticeable.  It  is  not  very  uncommon  to  see  a 
middle-aged  patient  with  an  inconspicuous  squint 
of  perhaps  two  or  three  degrees,  and  a  nearly- 
blind  eye.  He  usually  says  he  squinted  when  he 
was  a  boy,  but  gradually  grew  out  of  it. 

The  fusion  sense,  of  course,  cannot  be  developed 
during  the  continuance  of  a  deviation,  except  by 
artificial  means  (e.g.,  exercises  with  the  amblyo- 
scope).  If  it  be  prevented  from  developing  in 
infancy  and  early  childhood,  it  will  never  develop 
at  all  to  any  useful  extent.  It  is  true  that 
binocular  vision  of  a  sort  may,  in  exceptional 
cases,  be  acquired  as  late  as  eight  or  nine  years 
of  age,  but  it  is  so  feeble  that  it  is  powerless  to 
maintain  the  normal  relative  direction  of  the  eyes 
in    the  presence   of   uncorrected  hypermetropia ; 


42 


CONVERGENT    SQUINT 


so  that  glasses  must  be  worn  throughout  life  to 
prevent  a  return  of  the  deviation. 

Age  at  which  the  deviation  first  appears.  —  I  n 
my  note-books  I  find  the  onset-age  recorded  in 
1,017  cases  of  unilateral  convergent  squint,  and 
in  178  alternating  cases. 

The  number  of  unilateral  cases  beginning  in 
each  year  of  life  was  as  follows  : — 


Before  1  year 

...     134  cases 

Between  1  and  2  years     ... 

...     186       „ 

2    „    3      „         

...     247 

»        3    „     4      »         

...     189       „ 

„        4    „     5      „        

...     113 

»        5    „    6     , 

■  •■       73       ,, 

After  6  years 

...       75       » 

It  will  be  seen  that  in  nearly  75  per  cent,  of 
the  cases  the  deviation  appeared  before  the  end 
of  the  fourth  year,  and  in  less  than  7 h  per  cent, 
its  advent  was  delayed  until  after  the  sixth  year. 

The  alternating  cases  work  out  as  follows  : — 


Before  1  year 

..     61  cases 

Between  1  and  2  years 

-•     34       „ 

2    „     3     »           

23       „ 

3    „    4     »           

••     29       „ 

4    „     5     »           

•  •      n       » 

„        5    ,.    6    »           

••       6       » 

After  6  years 

■•      14      „ 

In  more  than  53  per  cent,  of  these  alternating 
cases  the  deviation  was  seen  before  the  end  of  the 
second  year.  This  high  proportion  is  due  to  the 
fact  that  the  essentially  alternating  squints  appear 
in  early  infancy. 


CONVERGENT    SQUINT  43 

Refractive  error  in  cases  of  convergent  squint. — 
In  infancy  and  early  childhood  hypermetropia  is 
the  normal  refractive  condition,  myopia  or  even 
emmetropia  being  then  very  uncommon.  In  the 
absence  of  the  controlling  influence  of  the  fusion 
sense,  the  state  of  the  refraction  is  the  main  factor 
in  determining  whether  the  eyes  shall  deviate 
inwards  or  outwards  (see  chapter  iv.).  It  is  not 
surprising,  therefore,  that  convergent  squinters 
are  nearly  always  hypermetropic,  and  very  fre- 
quently suffer  from  hypermetropic  astigmatism 
also. 

I  have  notes  of  1,636  cases  of  convergent 
squint  which  are  available  for  the  present 
enquiry. 

In  twenty-three  of  these  cases,  or  about  \\ 
per  cent.,  both  eyes  were  myopic.  I  have  not 
included  these  in  the  subjoined  tables. 

I  have  arranged  the  1,384  cases  of  unilateral 
convergent  squint  in  groups,  according  to  the 
number  of  dioptres  of  hypermetropia  in  the 
lowest  meridian  of  the  fixing  eye. 

I  have  calculated  the  average  refractive  error 
in  the  highest  and  in  the  lowest  meridian  of 
each  eye.  In  about  three-fourths  of  these  cases 
the  age  at  which  the  squint  was  first  seen  was 
recorded  on  the  case  sheets.  The  table  shows 
the  number  of  cases  found  in  each  group,  and 
the  average  onset-age. 

The  229  cases  of  alternating  convergent  squint 


44 


CONVERGENT    SQUINT 


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CONVERGENT    SQUINT  45 

are  similarly  tabulated,  except  that  they  are 
arranged  in  groups  according  to  the  number  of 
dioptres  of  hypermetropia  in  the  right  eye. 

Astigmatism  in  unt 'lateral  convergent  squint. 
—In  the  1,384  cases  I  found  the  proportion  of 
astigmatic  to  non-astigmatic  eyes  to  be  as 
follows  : — 

Fixing  eyes.  Deviating  eyes. 

No  astigmatism         ...  561  4QI 

Astigmatism  ...  823  983 

But  a  very  large  proportion  of  people  whose 
eyes  are,  for  all  practical  purposes,  normal,  have 
at  least  half  a  dioptre  of  astigmatism.  It  would 
only  be  misleading  to  expect  the  eyes  of  squinters 
to  conform  to  a  higher  standard  than  those  of 
normal-sighted  people.  If  we  disregard  astig- 
matism which  does  not  exceed  0*5  d,  we  get 
the  following  results  : — 

Fixing  eyes.  Deviating  eyes. 

Astigmatism  not  over  0.5  D  836  628 

Astigmatism  over  0-5  D     ...         547  756 

On  comparing  the  degree  of  refractive  error 
in  the  two  eyes  in  each  of  the  1,384  unilateral 
cases  we  find  : — 

Isometropia         4-7  cases. 

Anisometropia 957  cases. 

Or,  disregarding  differences  which  do  not 
exceed  0*5  d — 

Anisometropia  not  exceeding  05  D    663  cases. 

Anisometropia  exceeding  o"5  D  721  cases. 


46 


CONVERGENT    SQUINT 


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CONVERGENT    SQUINT  47 

These  alternating  cases  show  a  much  lower 
percentage  of  astigmatic  eyes  than  the  unilateral 
cases : — 

Right  eye.  Left  eye. 

No  astigmatism  114  II2 

Astigmatism "5  "7 

If  we  disregard  astigmatism  which  does  not 
exceed  0*5  d,  we  find  : — 

Right  eye.         Left  eve. 

Astigmatism  not  over  0-5  D 14°  J4X 

Astigmatism  exceeding  0-5  d  ...         89  88 

A  comparison  of  the  refraction  of  the  two  eyes 
in  each  of  the  229  alternating  cases  shows  : — 

Isometropia         131  cases. 

Anisometropia 98  cases. 

Or,  disregarding  differences  which  do  not 
exceed  0*5  d  : — 

Anisometropia  not  exceeding  o-5  D 185  cases. 

Anisometropia  exceeding  o-5  D  44  cases. 

The  relative  frequency  of  squint  was  the  subject 
of  a  careful  enquiry  which  Mr.  R.  E.  Hanson, 
oculist  to  the  Education  Department  of  the 
London  County  Council,  has  been  kind  enough 
to  undertake  at  my  request.  During  the  last  two 
years  10,239  school  children  have  been  examined 
in  the  Marylebone  and  the  Tower  Hamlets  dis- 
tricts. 253  of  these  children  exhibited  a  constant 
squint.  In  231  of  the  cases  the  squint  was  con- 
vergent, and  in  22  cases  divergent.  The  test 
used  was  the  mirror  test  described  on  page  80. 


48 


CHAPTER  IV. 
THE  .ETIOLOGY  OF  CONVERGENT  SQUINT. 

/Many  curious  suggestions  have,  in  former 
times,  been  made  as  to  the  cause  of  squint,  such 
as  "  an  evil  disposition,"  naughtiness,  imitating 
other  members  of  the  family  who  squint,  the 
habit  of  turning  the  eye  to  look  at  a  curl  or 
ribbon  on  one  side  of  the  face,  &c.  The  first 
definite  theory,  which  was  almost  universally 
accepted,  attributed  convergent  squint  to  a 
shortening  of  the  internal  recti.  The  natural 
corollary  of  this  was  that  the  affection  might 
be  cured  by  dividing  these  muscles  or  their 
tendons.  The  theory  and  its  practical  applica- 
tion seemed  so  plausible  and  simple  that  an  age 
of  indiscriminate  muscle-cutting  ensued.  When 
the  disastrous  results  of  this  practice  were  begin- 
ning to  be  recognised,  Donders  published  his 
great  work,  and  his  "accommodation  theory"  of 
the  cause  of  squint  immediately  came  into  vogue. 
It  will  be  well  to  examine  these  two  theories 
n  detail. 

uscle  theory.  —  Many   writers   on    convergent 
squint  have  attributed  the  anomaly  to  an  undue 


THE    /ETIOLOGY    OF    CONVERGENT    SQUINT         49 

shortness  or  tightness  of  the  internal  recti,  to  a 
faulty  insertion  of  the  tendons  of  these  muscles, 
or  to  a  paresis  of  the  external  recti.  To  an 
observer  who  sees  in  a  case  of  convergent  squint 
only  its  most  obvious  symptom,  viz.,  the  abnormal 
convergence,  it  may  seem  reasonable  to  attribute 
this  deformity  to  a  defect  of  the  muscles  which 
move  the  eyes.  A  little  investigation  ought  to 
convince  anyone  of  the  falsity  of  this  view. 

Of  1,523  cases  of  convergent  squint  in  which 
I  investigated  this  point,  I  found  the  power  of 
abversion  (outward  rotation)  of  each  eye  tested 
separately  to  be  quite  perfect  in  81  per  cent.  ; 
in  the  remaining  19  per  cent,  the  power  of 
abversion  was  sub-normal,  but  the  defect  in  most 
of  these  19  per  cent,  was  slight.  This  alone 
would  seem  sufficient  to  demonstrate  that,  in  81 
per  cent,  of  convergent  squints  at  least,  there  is 
no  undue  shortness  of  the  internal  recti  or  paresis 
of  the  external  recti  muscles.  In  the  19  per  cent, 
the  deviation  had,  in  the  vast  majority  of  cases, 
lasted  several  years,  and  the  average  degree  of 
the  defect  of  abversion  was  directly  proportionate 
to  the  duration  of  the  deviation.  The  defect  of 
abversion  in  nearly  all  the  19  per  cent,  of  cases 
would  therefore  appear  to  be  due  to  secondary 
changes  in  the  muscles  and  fascia;,  the  result 
of  the  long  continuance  of  the  deviation,  not  its 
cause.  One  wonders  that  these  secondary  changes 
take  place  so  seldom  and  to  such  a  slight  extent. 


50        THE    /ETIOLOGY    OF    CONVERGENT    SQUINT 

It  is  a  matter  of  common  observation  that  a 
convergent  squint  very  frequently  disappears,  or 
the  eyes  even  diverge,  during  general  anaesthesia. 

Occasionally  a  very  high  degree  of  convergence 
disappears  when  the  accommodation  is  paralysed 
by  atropine.  It  always  reappears  when  the  effect 
of  the  atropine  has  passed  off. 

Of  cases  of  convergent  squint  which  are  treated 
with  glasses  alone,  in  about  30  per  cent.1  the  eyes 
eventually  become  approximately  "straight,"  and 
remain  so  as  long  as  the  glasses  are  worn. 

These  facts  scarcely  seem  compatible  with  a 
muscular  origin  of  squint. 

Bonders  theory. — When  a  person  with  normal 
emmetropic  eyes  looks  at  an  infinitely  distant 
object,  such  as  a  star,  the  visual  axes  are  parallel, 
and  the  static  refraction  of  each  eye  is  sufficient 
to  focus  the  image  of  the  object  on  its  retina.  If 
the  person  now  looks  at  an  object  only  a  foot 
away  from  him  he  must  turn  the  eyes  slightly 
inwards  (convergence),  in  order  that  both  visual 

1  1  have  no  statistics  of  my  own  showing  the  proportion 
of  "  cures  "  effected  by  glasses  alone,  because  I  do  not  rely 
solely  upon  optical  correction  and  operation.  Of  ninety- 
four  cases  of  unilateral  convergent  squint  quoted  by 
Holthouse,  the  deviation  was  gradually  overcome,  and  the 
eyes  remained  "  straight  "  so  long  as  glasses  were  worn  in 
twenty-nine  cases,  or  308  per  cent.  Lang  and  Barrett 
(R.L.O.H.  Reports,  vol.  xii.)  had  thirty-seven  cures  by 
glasses  out  of  102  cases,  or  36-3  per  cent.  But  in  this 
series  all  cases  in  which  less  than  five  degrees  deviation 
remained  were  considered  cured. 


THE    ^ETIOLOGY    OF    CONVERGENT    SQUINT       5  I 

axes  may  meet  at  the  object.  At  the  same  time 
each  eye  must  be  focussed  for  near  vision  (accom- 
modation), in  order  that  the  object  may  be  seen 
distinctly.  These  two  acts,  accommodation  and 
convergence,  being  always  performed  together, 
have  become  "  associated  "  by  hereditary  habit, 
so  that  it  is  difficult  to  converge  without  accom- 
modating or  to  accommodate  without  converging. 

Hypermetropic  eyes  in  a  state  of  rest  are  out 
of  focus  even  for  distant  objects,  and  still  more  so 
for  near  objects.  A  hypermetrope,  therefore,  in 
order  to  see  distinctly,  must  accommodate  in 
distant  vision  to  a  degree  corresponding  to  the 
amount  of  his  hypermetropia.  In  near  vision  he 
must  accommodate  both  for  the  hypermetropia 
and  for  the  nearness  of  the  object.  There  is  a 
tendency  for  a  proportionate  abnormal  conver- 
gence to  be  associated  with  this  abnormal  effort 
of  accommodation.  Donders  considered  this 
tendency  to  be  the  cause  of  convergent  squint, 
and  he  advised  optical  correction  of  the  hyper- 
metropia with  a  view  to  curing  the  squint. 

By  this  chain  of  observation  and  reasoning  the 
great  physiologist  let  the  first  ray  of  light  into 
this  dark  corner  of  ophthalmology,  and  gave  the 
first  indication  for  a  rational  treatment  of  con- 
vergent squint.  But  he  was  mistaken  in  sup- 
posing hypermetropia  to  be  the  fundamental 
cause  of  the  malady. 

The    vast     majority     of    children    are    hyper- 


52         THE    .-ETIOLOGY    OF    CONVERGENT    SQUINT 

metropic.  Of  these  hypermetropes  only  a  small 
percentage  present  themselves  at  the  clinics, 
whereas  nearly  all  the  squinters  come  at  some 
time  or  other.  Yet,  even  there,  one  sees  at  least 
a  dozen  hypermetropes  who  do  not  squint  for 
one  who  does.  This  cannot  be  explained  on  the 
hypothesis  that  the  severe  cases  of  hypermetropia 
especially  tend  to  cause  squint,  because  statistics 
show  that  this  is  not  the  case  (see  tables  i.  and 
ii.,  chapter  iii.). 

It  is  usually  stated  that  moderate  degrees  of 
hypermetropia  are  especially  prone  to  be  asso- 
ciated with  squint.  This  is  explained  by  saying 
that  a  child  with  moderate  hypermetropia  will 
accommodate  in  order  to  see  distinctly.  He 
only  manages  to  make  the  extra  accommodative 
effort  by  bringing  into  play  also  an  associated 
effort  of  convergence.  So  that  he  sees  distinctly 
with  one  eye  and  turns  in  the  other.  But,  it  is 
said,  if  the  hypermetropia  be  excessive,  he  will 
not  be  able  to  accommodate  sufficiently,  so  that 
he  gives  up  the  struggle,  and  neither  sees  dis- 
tinctly nor  squints. 

But  this  ingenious  argument  is  based  on  false 
premises.  Moderate  degrees  of  hypermetropia 
are  more  common  than  high  degrees,  not  only 
in  those  who  squint,  but  also  in  those  who  do 
not  squint.  I  looked  through  my  out-patient 
letters  at  the  West  Ham  Hospital  for  about 
eighteen    months,    and    tabulated    all    the    cases 


THE    ETIOLOGY    OF    CONVERGENT    SQUINT         53 

of  hypermetropia,  without  squint,  in  which  the 
refractive  error  was  measured  by  retinoscopy 
under  atropine.  I  tabulated  the  cases  according 
to  the  degree  of  hypermetropia,  and  worked  out 
the  percentage  number  of  eyes  in  each  grade.1 

The  results,  in  the  cases  in  which  the  hyper- 
metropia was  more  than  2  d,  were  found  to 
correspond  very  closely  with  my  squint  statistics 
treated  in  the  same  way.  The  proportion  of 
cases  with  less  than  2  d  was  lower  among  the 
non-squinters  than  among  the  squinters.  Also 
the  average  degrees  of  astigmatism  were  higher 
among  the  non-squinters  than  among  the  squin- 
ters. This  is  evidently  due  to  the  fact  that  most 
of  the  non-squinters  were  patients  who  sought 
advice  on  account  of  headaches  or  visual  defect. 

It  will  thus  be  seen  that  the  degree  of  the 
refractive  error  has  very  little  to  do  with  the 
question  of  whether  the  patient  shall  or  shall  not 
squint  in  the  first  instance,  though,  of  course, 
when  the  squint  is  once  established,  the  refractive 
error  becomes  a  very  important  factor. 

A    high    degree   of  hypermetropia  has  no  in- 

1  In  cases  in  which  there  was  also  astigmatism,  the 
mean  between  the  highest  and  lowest  meridian  was  taken. 
I  have  since  compared  the  results  of  taking  the  highest 
meridian  only,  also  the  lowest  meridian  only.  The  number 
of  cases  taken  excludes  any  accidental  source  of  error.  A 
slight  defect  in  this  mode  of  comparison  will,  of  course, 
suggest  itself,  but  the  error  is  not  sufficiently  grave  to 
affect  the  main  results. 


54       THE    /ETIOLOGY    OF    CONVERGENT    SQUINT 

fluence  in  determining  an  early  onset  of  squint, 
as  is  conclusively  shown  by  the  following  table. 
In  the  unilateral  cases  I  have  taken  the  average 
of  the  highest  and  lowest  meridian  in  the  fixing 
eye,  and  in  the  alternating  cases  I  have  taken 
the  average  of  both  eyes. 

Less  than   +2  D   average   age  of  onset  =  2^47  years.1 

+  2  D  to  +4  D  „  „  „  =   2-85          „ 

+4  D  to  +6  D  „  „  „        =  2-92       „ 

More  than  +6  D  „  „  „        =  -  2*96       „ 

A  great  many  children  who  suffer  from  con- 
vergent squint  have  no  more  than  the  normal 
degree  of  hypermetropia,  while  1  or  2  per  cent, 
are  actually  myopic. 

It  is  evident,  then,  that,  though  hypermetropia 
stands  in  some  close  setiological  relation  to  con- 
vergent squint,  it  is  not  the  essential  cause  of  the 
anomaly. 

/Etiology  of  Convergent  Squint. 

For  the  sake  of  clearness,  I  will  first  state  my 
proposition,  and  give  the  proofs  afterwards. 

In  a  case  of  convergent  squint  there  is,  in 
addition  to  the  most  obvious  symptom,  the  de- 
formity, always  a  defect  of  the  fusion  faculty,  and 
there  is  nearly  always  a  suppression  of  the  vision 

of  the  deviating  eye. 

j 

1  The  average  age  of  onset  is  low  in  these  squinters,  with 
less  than  2  d  of  hypermetropia,  because  cases  of  essen- 
tially alternating  squint  are  included  in  this  table. 


THE    /ETIOLOGY    OF    CONVERGENT    SQUINT         55 

In  the  human  infant,  the  motor  coordinations 
of  the  eyes  are  already  partially  developed  at 
birth.  During  the  first  few  months  of  life  these 
serve  (in  the  absence  of  any  disturbing'  influence) 
to  maintain  approximately  the  normal  relative 
directions  of  the  eyes.  Soon  the  fusion  faculty 
begins  to  develope.  I  have  found  distinct  evi- 
dence of  binocular  vision  in  the  sixth  month. 
Normally  the  development  of  the  fusion  faculty 
is  well-advanced  by  the  twelfth  month,  and  com- 
plete before  the  end  of  the  sixth  year.  When  the 
fusion  faculty  has  begun  to  develope,  the  instinctive 
tendency  to  blend  the  images  formed  in  the  two 
eyes — -the  "desire  for  binocular  vision,"  as  it  is 
called — will  keep  the  eyes  "  straight."  When  the 
fusion  faculty  is  fairly  well  developed,  neither 
hypermetropia,  nor  anisometropia,  nor  hetero- 
phoria  can  cause  squint.  In  fact,  then,  nothing 
but  an  actual  muscular  paralysis  can  cause  an 
eye  to  deviate,  in  which  case  the  resulting  diplopia 
is  intolerable.  Sometimes,  however,  owing  to  a 
congenital  defect,  the  fusion  faculty  developes 
later  than  it  should,  or  it  developes  very  imper- 
fectly, or  it  may  never  develope  at  all.  Then, 
in  this  case,  there  is  nothing  but  the  motor 
coordinations  to  preserve  the  normal  relative 
directions  of  the  eyes,  and  anything  which  dis- 
turbs the  balance  of  these  coordinations  will 
cause  a  permanent  squint.  Thus  the  essential 
cause  of  squint  is  a  defect  of  the  fusion  faculty. 


'  In  the  presence  of  this  fundamental  cause,  the 
eyes  are  in  a  state  of  unstable  equilibrium,  ready 
to  squint  either  inwards  or  outwards  on  slight 
provocation.  This  provocation  may  be  supplied 
by:- 

(i)  Hypermetropia.  — As  already  explained, 
uncorrected  hypermetropia  causes  a  tendency  to 
abnormal  dynamic  convergence  of  the  visual  axes. 
In  the  vast  majority  of  cases  of  hypermetropia  the 
fusion  sense  is  perfect,  so  that  this  tendency  is 
kept  in  check  and  the  child  does  not  squint.  If, 
however,  the  fusion  sense  is  deficient,  the  eyes  are 
free  to  yield  to  this  tendency,  and  a  convergent 
squint  is  established.  In  the  cases  in  which 
hypermetropia  is  the  immediate  exciting  cause, 
the  abnormal  convergence  is  at  first  entirely  dyna- 
mic, static  convergence  being  nil.  The  squint 
is  at  first  occasional — when  the  child  is  looking 
at  nothing  in  particular,  relaxing  the  accom- 
modation, the  deviation  disappears.  Optical  cor- 
rection of  the  refractive  error  at  this  period  often 
cures  the  deviation.  But  if  nothing  is  done,  the 
excessive  exercise  of  the  function  of  dynamic  con- 
vergence causes  an  abnormal  static  convergence 
to  appear.  So  that  the  visual  axes  are  convergent 
even  when  the  eyes  are  completely  at  rest.  At 
this  period  optical  correction  does  not  cause  an 
immediate  disappearance  of  the  deviation.  It 
may  gradually  do  so,  perhaps,  after  the  glasses 
have  been  worn  for  a  few  weeks  or  months. 


THE    /ETIOLOGY    OF    CONVERGENT    SQUINT         57 

In  cases  in  which  the  fusion  sense  is  present 
but  feeble,  it  may  be  strong  enough  to  resist  the 
strain  of  uncorrected  hypermetropia  during  in- 
fancy, but  may  give  way  when  the  child's  atten- 
tion is  directed  to  his  first  lessons.  There  is 
scarcely  ever  diplopia.  Rarely  one  meets  with 
a  child  who,  when  patiently  questioned,  admits 
that  he  sees  a  second  image.  This  faint  diplopia 
persists,  but  is  never  annoying. 

During  the  first  few  weeks  of  life,  even  in  cases 
of  very  high  hypermetropia,  the  motor  coordina- 
tions suffice  to  maintain  approximately  the  normal 
relative  directions  of  the  eyes,  until  the  developing 
fusion  faculty  takes  control  and  makes  everything 
safe.  Probably  the  infant  does  not  use  his  ac- 
commodation much  at  this  early  period.  But,  in 
rare  instances,  hypermetropia  may  cause  a  squint 
before  the  period  at  which  the  child  should 
normally  begin  to  acquire  the  fusion  faculty  {e.g., 
Case  A,  503,  page  151).  In  such  a  case,  if  the 
deviation  is  allowed  to  persist,  the  natural  de- 
velopment of  the  fusion  faculty  will,  of  course, 
be  prevented. 

(2)  Anisometropia,  and  the  rare  congenital 
amblyopia,  predispose  to  squint  by  making  bin- 
ocular vision  more  difficult.  One  occasionally  sees 
a  case  of  squint  in  which  the  fixing  eye  is  approxi- 
mately emmetropic  and  the  deviating  eye  has 
perhaps  10  or  15  d  of  myopia. 

(3)  If   the  fusion  sense  be  perfect,  a  want  of 


58       THE    /ETIOLOGY    OF    CONVERGENT    SQUINT 

balance  of  the  motor  apparatus  of  the  eyes  will 
cause  heterophoria  but  not  squint.  But  in  the 
absence  of  the  controlling  influence  of  the  fusion 
sense,  this  motor  imbalance  is  free  to  cause  an 
actual  deviation.  This  is  seen  when,  in  examin- 
ing a  case  of  heterophoria,  fusion  is  temporarily 
rendered  impossible  by  means  of  Maddox  rod, 
coloured  glasses,  &c. 

(4)  Specific  fevers,  especially  whooping  cough, 
are  often  assigned  by  the  parents  as  the  cause  of 
the  squint.  One  usually  hears  that  the  child  was 
seen  to  squint  during  convalescence,  that  the 
squint  was,  at  first,  occasional,  and  that  it  became 
constant  after  a  few  weeks.  These  children 
usually  have  a  good  deal  of  hypermetropia.  The 
mode  of  origin  of  these  squints  is  probably  as 
follows:— The  fusion  sense  is  defective  (shown 
by  the  absence  of  diplopia),  but  the  motor  co- 
ordination, or  some  slight  degree  of  fusion  sense, 
has  hitherto  sufficed  to  prevent  the  occurrence  of 
a  deviation.  During  convalescence  the  child  is 
given  picture-books.  Owing  to  the  muscular 
enfeeblement  caused  by  his  illness,  he  is  unable 
to  accommodate  so  well  as  formerly.  The  exces- 
sive effort  of  accommodation  upsets  the  unstable- 
equilibrium.  At  first^the  abnormal  convergence 
is  dynamic  only,  and  disappears  when  the  child 
relaxes  his  accommodation.  A  pair  of  spectacles 
at  this  period  often  brings  about  a  cure.  Hut  if 
he    opportunity    be    lost    a    static    convergence 


THE    ^ETIOLOGY    OF    CONVERGENT    SQUINT         59 

appears,    and    what    was    merely    a    premonitory 
occasional  squint  becomes  constant. 

As  a  contrast  to  these  cases,  it  occasionally  happens 
that  a  child,  whose  fusion  faculty  is  perfect,  suffers 
from  a  paresis  of  an  external  ocular  muscle  after 
diphtheria.  The  child  complains  of  persistent  and 
annoying  diplopia  until  the  muscle  recovers  its  func- 
tion. I  recently  had  the  opportunity  of  watching  such 
a  case.  The  patient,  a  little  girl,  aged  five  years,  had 
paresis  of  the  right  external  rectus  muscle  after 
diphtheria.  She  volunteered  the  statement  that  she 
saw  "two  nurses"  and  that  "things  looked  funny." 
She  was  uncertain  in  her  movements  in  running  about, 
and  often  made  a  false  shot  in  picking  up  a  ball 
from  the  floor.  When  I  gave  her  a  picture  book  to 
look  at,  she  covered  the  affected  eye  with  her  hand. 
When  I  saw  her  a  few  days  later,  she  kept  her  head 
constantly  turned  to  the  right,  evidently  to  enable  her 
to  blend  the  images.  The  case  completely  recovered 
in  about  seven  weeks. 

(6)  Violent  mental  disturbance,  caused  by  severe 
fright,  "  convulsion-fits,"  &c,  may,  in  the  absence 
of  the  fusion  faculty,  upset  the  equilibrium  of  the 
convergence  centre.  The  convergence  is  static, 
it  appears  immediately,  and  is  constant  from 
the  first.  Refractive  error  is  not  an  important 
feature.  A  large  percentage  of  these  cases  are 
alternating. 

Injury  during  birth. — Now  and  then  one  sees 
a  case  in  which  the  power  of  abversion  of  an 
eye  has  been  absent  since  earliest  infancy, 
probably  owing  to  injury  to  the  sixth  cranial 
nerve  during  birth.      In  most  of  these  cases  the 


60       THE    .ETIOLOGY    OF    CONVERGENT    SQUINT 

position  of  the  eye  prevents  the  natural  develop- 
ment of  the  fusion  sense.  If  no  precautions  are 
taken  the  eye  may  become  extremely  amblyopic. 
Hereditary  influence  is  a  marked  feature  in  any 
series  of  cases  of  convergent  squint.  In  1,373 
cases  of  squint  in  which  I  was  able  to  get  probably 
reliable  information,  there  was  a  history  of  squint 
in  parent,  grand-parent,  brother,  or  sister  of  the 
patient  in  no  less  than  711,  or  5  1  78  per  cent. 

Proof  that  the  Essential  Cause  of  Squint  is  a 
Defect  of  the  Fusion  Faailty. 

If  a  pair  of  object-slides  such  as  fig.  17  be  put 
in  the  amblyoscope,  a  person  with  a  normal  pair 
of  eyes  will  be  able  to  blend  the  two  imperfect 
images  into  one  complete  picture.  If  the  angle  of 
the  instrument  be  varied  the  eyes  will  converge, 
or  (to  a  certain  extent)  diverge  also,  in  order  to 
follow  the  objects  and  maintain  fusion. 

Now  take  a  young  patient  with  an  ordinary 
unilateral  convergent  squint,  and  good  vision  in 
each  eye.  Adjust  the  amblyoscope  to  suit  the 
angle  of  his  deviation.  He  will  only  see  with  the 
fixing  eye,  the  vision  of  the  squinting  eye  being 
suppressed.  If  the  suppression  be  now  overcome 
by  the  method  described  in  chapter  viii.,  he 
will  see  the  two  imperfect  images  simultaneously. 
After  a  little  practice,  a  position  can  usually  be 
found  in  which  the  two  imperfect  images  overlap, 
so  that  the  patient  sees  them  blended  into  one 


THE    ETIOLOGY    OF    CONVERGENT    SQUINT         6 1 

complete  picture.  But  they  are  blended  only  in 
that  one  position.  If  the  angle  of  the  instrument 
be  again  altered,  the  images  at  once  separate — 
no  effort  can  be  made  to  maintain  fusion.  This 
shows  that,  though  the  fusion  faculty  is  not 
quite  absent,  it  is  exceedingly  ill-developed.  The 
brilliant  results  obtained  in  these  cases  by  train- 
ing the  fusion  faculty  at  an  early  age,  strongly 
support  the  view  that  the  defect  of  this  faculty 
was  the  fundamental  factor  in  permitting  the 
deviation  to  occur. 

Consider  next  a  typical  case  of  essentially 
alternating  squint.  The  visual  acuity  of  each  eye 
is  perfect  ;  there  is  no  important  refractive  error  ; 
the  movements  of  each  eye  separately  are  perfect. 
Why  then  does  such  a  pair  of  eyes  squint  ?  The 
muscle  theory  cannot  explain  it,  because  there  is 
no  motor  defect  of  either  eye.  Hypermetropia 
cannot  be  the  cause,  because  there  is  little  or 
no  refractive  error ;  moreover,  the  wearing  of 
correcting  glasses  usually  has  no  effect  upon  the 
deviation.  No  theory  hitherto  put  forward  has 
satisfactorily  explained  these  cases.  But,  if  the 
condition  of  the  fusion  faculty  be  examined,  the 
mystery  is  cleared  up  at  once.  Let  a  patient  with 
an  essentially  alternating  squint  look  at  a  pair  of 
object  slides  such  as  fig.  16  in  the  amblyoscope. 
When  the  objects  are  very  far  apart,  he  may  be 
able  to  see  both.  But  when  they  are  made  to 
approach  each  other,  he  loses  sight  of  one  of  them. 


62       THE    AETIOLOGY    OF    CONVERGENT    SQUINT 

No  amount  of  practice  will  ever  enable  an  essen- 
tially alternating  squinter  to  see  the  two  devices 
simultaneously  when  they  are  close  together, 
much  less  to  blend  them.  There  is  a  congenital 
total  absence  of  the  fusion  faculty. 

The  great  frequency  with  which  squint  occurs 
in  more  than  one  member  of  a  family  has  enabled 
me  to  obtain  still  more  direct  evidence.  When  I 
have  had  a  child  under  treatment  for  convergent 
squint,  I  have,  in  very  many  instances,  induced 
the  mother  to  bring  me  also  for  examination  a 
younger  brother  or  sister  of  the  patient,  who  had 
not  hitherto  squinted.  I  examined  the  fusion 
sense  of  all  except  the  most  intractable  of  these 
brothers  and  sisters  of  squinters  with  the  amblyo- 
scope.  I  have  been  able  to  follow  the  subsequent 
history  of  157  of  these  children.  In  106  cases  I 
found  the  fusion  faculty  well  developed.  Not  one 
of  these  has  subsequently  squinted.  Of  thirty- 
seven  cases  in  which  the  note  was  "  doubtful," 
six  have  since  squinted.  Of  fourteen  cases  in 
which  my  note  said  "  fusion  faculty  very  defi- 
cient," eight  have  since  developed  a  constant 
squint,  and  another  child  is  said  to  cross  her 
eyes  occasionally, 


63 


CHAPTER   V. 
AMBLYOPIA,   CONGENITAL   AND   ACQUIRED. 

The  amblyopia  discussed  in  this  chapter  is  a 
partial  blindness  of  an  eye  in  which  the  most 
careful  examination  of  the  fundus  and  media 
reveals  nothing  sufficient  to  account  for  the 
defect.  This  amblyopia  persists  after  accurate 
optical  correction  of  any  refractive  error  which 
may  be  present.  It  may  be  either  congenital  or 
acquired. 

It  will  be  well  to  consider  congenital  ambly- 
opia and  the  acquired  form  separately,  before 
discussing"  the  amblyopia  so  often  found  in  cases 
of  convergent  squint. 

Congenital  amblyopia,  apart  from  squint,  is  very 
seldom  met  with.  One  should  not  accept  a  case 
as  being  one  of  congenital  amblyopia,  unless 
careful  questioning  of  intelligent  and  observant 
parents  makes  it  certain  that  the  patient  has 
never  squinted  as  a  child. 

In  the  course  of  examining  the  refraction  of 
many  thousands  of  patients  who  have  never 
squinted,  I  have  only  met  with  twenty-three  cases 
of  amblyopia,  of  ~  or  higher,  which  I  have  felt 
justified  in  regarding  as  congenital.      These  cases 


64  AMBLYOPIA 

are  described  in  detail  in  the  appendix   (p.  219). 
They  have  certain  peculiarities  in  common.      The 
fundus    and    media    are     normal    in    appearance. 
The  fields  of  vision,  both  for  white  and  colours, 
are  full.     There  is  no  scotoma.      Central  colour 
perception  is  normal.    The  peripheral  form  vision, 
up  to  within  20°  of  the  fixation  point,  is  normal.1 
So  that  the  defect  would  seem  to  consist  in  a  want 
of   due     preponderance    of    the    macular    region, 
and  not  in  a  general  lowering  of  the  sensibility 
of  the   visual    apparatus.        In  no   case   was    the 
vision  of   the  amblyopic  eye  less  than   eGo-      But 
the  most  remarkable  feature  of  these  cases  is  that 
the   defect  is  confined  to  one  eye,  which  almost 
invariably  has  a  high  degree  of  compound  hyper- 
metropic  astigmatism  ;    while   the  other  eye  has 
normal   vision,    and   either    normal    refraction    or 
hypermetropia,    without    any    notable    degree    of 
astigmatism."      In  many  of  the  cases   the   fusion 
faculty  was  examined  with  the  amblyoscope.      It 
was  found  to  be  well  developed. 

1  For  the  purpose  of  testing  the  peripheral  form  vision, 
I  use  three  metal  screens  about  two  inches  square,  each 
showing  a  white  O  on  a  black  ground.  The  letters  on  the 
three  screens  are  of  different  sizes.  By  a  simple  mechanical 
device  the  O  is  readily  converted  into  a  C.  The  screens 
are  successively  attached  to  the  object-carrier  of  a  peri- 
meter. The  investigation  is  proceeded  with  just  as  in 
mapping  out  the  fields  of  vision,  the  patient  being  required 
each  time  to  say  whether  the  letter  is  O  or  C.  In  this  way 
three  zones  are  mapped  out  on  the  chart.  This  method 
though  very  valuable  for  purposes  of  scientific  investigation, 
is  too  tedious  for  ordinary  clinical  use. 


CONGENITAL    AND    ACQUIRED  65 

There  is  another  small  group  of  cases  in  which 
the  amblyopia  may  almost  certainly  be  regarded 
as  congenital.  Table  iii.,  p.  76,  includes  only  cases 
of  squint  in  which  my  treatment  was  begun  soon 
after  the  first  appearance  of  the  deviation  and 
was  carried  out  thoroughly,  so  that  there  was 
scarcely  a  possibility  of  any  acquired  amblyopia. 
It  will  be  seen  that  the  vast  majority  of  these 
patients  have,  with  optical  correction,  perfect 
vision  in  each  eye.  In  seventeen  cases  out  of 
the  193  the  vision  of  the  squinting  eye  was  f  or 
Y^.  In  nine  cases  it  was  ~  or  A-  In  two  cases 
it  was  36g  or  £0-  In  no  case  was  the  vision  lower 
than  <&,  and  in  no  case  was  the  power  of  central 


2  I  wish  to  avoid  vague  speculation.  But  the  thought 
obviously  occurs  to  one  — Is  it  possible  that,  in  some  of 
these  cases  in  which  I  have  regarded  the  amblyopia  as 
congenital,  it  may  really  have  been  acquired  through  the 
patient's  confining  his  attention  to  the  sharp  image,  even 
though  this  is  fused  with  the  blurred  image  of  the  astig- 
matic eye  ?  The  fact  that  the  amblyopia  is  always  confined 
to  one  eye  lends  colour  to  the  suggestion.  The  possibility 
of  confining  one's  attention  to  the  image  formed  in  one 
eye,  and  yet,  at  the  same  time,  exercising  binocular  vision, 
is  easily  demonstrated.  Let  one  imitate  the  refractive  con- 
dition of  one  of  these  patients  by  wearing  a  high  cylin- 
drical lens  before  one  of  one's  own  eyes,  then  read  the  test 
types  with  both  eyes  open.  By  confining  the  attention 
to  the  naked  eye,  one  reads  f.  In  reading  a  book  one 
soon  learns  to  disregard  entirely  the  blurred  image  seen 
through  the  cylinder.  At  the  same  time,  it  is  easy  to 
convince  oneself  that  one  is  exercising  binocular  vision — 
prism,  base  in,  produces  diplopia ;  prism,  base  out,  causes 
convergence  of  the  visual  axes  in  order  to  blend  images  ; 
four-dot  test,  &c. 


66  AMBLYOPIA 

fixation  absent.  On  referring  to  my  case  books, 
I  find  that,  in  the  more  amblyopic  cases,  the 
defective  eye  nearly  always  had  a  high  degree  of 
compound  hypermetropic  astigmatism,  while  the 
other  eye  had  perfect  vision  and  nearly  always 
simple  hypermetropia  without  any  notable  astig- 
matism. These  cases  are  described  in  the 
appendix. 

Amblyopia  acquired  from  disuse  (amblyopia 
ex  anopsia).  In  a  case  of  convergent  squint, 
even  though  the  vision  of  each  eye  separately  be 
perfect,  the  patient  will,  when  both  eyes  are  open, 
only  see  with  the  "  straight "  eye.  The  impres- 
sions received  by  the  deviating  eye  are  mentally 
"  suppressed."  In  the  case  of  a  young  child  with 
a  constant  unilateral  squint,  the  result  of  this 
disuse  of  the  deviating  eye  is  that  its  visual  acuity 
gradually  deteriorates.  This  deterioration  from 
disuse  is  the  more  rapid  the  younger  the  child,  so 
much  so  that  it  is  commonly  believed  that  an  eye 
which  squints  in  infancy  is  necessarily  very  blind. 
This  is  not  so,  as  table  iii.  clearly  shows.  A 
child  with  good  vision  in  each  eye,  who  developes 
a  constant  unilateral  squint  at  the  age  of  six  or 
eight  months,  will,  in  the  absence  of  proper  treat- 
ment, become  rapidly  blind  in  the  squinting  eye. 
This  loss  of  vision  in  the  infant's  deviating  eye  is 
so  rapid  that  the  power  of  central  fixation  is  often 
lost  within  eight  or  ten  weeks.  In  an  eye  which 
begins  to   squint   constantly  at  the  age  of,  say, 


CONGENITAL    AND    ACQUIRED  6j 

eighteen  months,  the  progress  of  the  blindness  is 
rapid,  but  much  less  so  than  in  a  younger  child. 
At  least  five  or  six  months  usually  elapse  before 
the  eye  loses  the  power  of  central  fixation.  An 
eye  which  begins  to  deviate  constantly  at  the  age 
of  three  years  seldom  quite  loses  the  power  of 
central  fixation  in  less  than  a  year.  I  have  never 
seen  central  fixation  lost  in  a  case  in  which  the 
squint  had  first  appeared  after  six  years  of  age. 
After  six  years  of  age  amblyopia  ex  anopsia 
seldom  takes  place  to  any  great  extent.  Acquired 
amblyopia  is  a  true  loss  of  vision,  not  a  failure  of 
the  function  to  develope,  as  is  shown  by  cases 
quoted  below. 

I  have  notes  of  several  cases  in  which  ignorant 
or  careless  parents  have  accidentally  performed 
upon  their  children  most  instructive  (but  disas- 
trous) experiments  bearing  upon  this  subject. 
Here  are  brief  notes  of  a  few  of  the  more  striking 
examples. 

CASE  A,  77.1— On  November  14,  1895,  I  saw,  at 
West  Ham,  a  girl,  aged  2  years  7  months.  She  had 
constant  convergent   squint   R.  E.   220.     The   mother 

1  The  letters  and  numbers  are  the  index  marks  of  the 
notes  in  my  squint  case-books.  In  the  case  notes  I  have 
used  certain  abbreviations,  some  of  which  may  require 
explanation,  e.g.,  "  C.S.R.E.  220"  means  "constant  uni- 
lateral convergent  squint,  the  angle  of  deviation  being  22° 
in  distant  vision  and  the  right  being  the  deviating  eye." 
"  V.R.E."  means  "  vision  of  the  right  eye."  After  glasses 
had  been  ordered,  the  angle  of  deviation  and  the  visual 
acuity  were  always  measured  with  the  glasses  on. 


68  AMBLYOPIA 

said  that  the  child  had  squinted  about  a  month.  The 
squint  was  nearly  alternating.  After  shading  L.  E.  for 
a  moment,  she  would  fix  with  R.  E.,  and  continue  to 
do  so  for  a  minute  or  two  after  removing  the  shade. 
Two  hours  after  putting  a  drop  of  atropine  into  the 
L.  E.  she  was  seen  to  squint  always  with  the  L.  E.  and 
fix  with  the  R.  E. 

November  21,  1895.  —  Retinoscopy  under  atropine 
each  eye  +  375  D  sph.  I  ordered  +  3  D  sph.  for 
constant  wear  ;  and  a  drop  of  liquor  atropinae  to  be 
put  into  the  L.  E.  only  every  morning.  Child  to  be 
seen  again  in  a  month. 

August  22,  1901. — The  child  is  brought  to  me  at  the 
West  Ham  Hospital.  I  have  not  seen  her  for  nearly 
six  years.  The  mother  has  no  recollection  of  having 
used  the  drops  for  the  L.  E.  She  says  the  child  wore 
the  glasses  for  about  a  year,  then  lost  them.  No 
treatment  since.  Child  is  now  aged  8  years  4  months. 
She  has  convergent  squint  R.  E.  170.  The  fixation  of 
the  R.  E.  is  lost.  Vision  of  the  R.  E.  is  reduced  to  the 
counting  of  fingers  at  5  feet. 

Case  D,  527.  October  16,  1900. — Boy,  aged  13 
months,  brought  to  Moorfields.  The  mother  said  he 
had  "  squinted  the  last  few  weeks."  Child  has  con- 
vergent squint  R.  E.  30°  about,  varies  slightly.  Good 
central  fixation  R.  E. 

October  23,  1900. — Retinoscopy  under  atropine  shows 
refractive  error  R.  E.  +  4  D  sph.  +  1  D  cyl.  ax.  vert., 
L.  E.  +  4  D  sph.  Ordered  glasses  0*5  D  less  than  the 
retinoscopy.  Ordered  guttaj  atropine  1  per  cent.  L.  E. 
only  every  morning. 

December  4,  1900. — Child  uses  unatropised  R.  E. 
always,  both  in  near  and  distant  vision,  and  squints 
with  atropised  L.  E.  Ordered,  stop  the  drops  and 
come  again  in  a  month. 

January  8,  1901. — Child  has  now  convergent  squint. 
180  with  the  glasses.  The  squint  alternates.  Ordered, 
wear  glasses  and  come  first  week  in  April. 


CONGENITAL    AND    ACQUIRED  69 

January  3,  1902. — Child  has  not  been  seen  for  a  year. 
Soon  after  last  visit  mother  says  he  lost  his  glasses. 
He  has  had  no  treatment  since.  There  is  now  con- 
vergent squint  R.  E.  320.  R.  E.  has  lost  the  power  of 
central  fixation.  With  L.  E.  bandaged,  child  sees  the 
1^  inch  ivory  ball  when  it  is  rolling  on  the  floor,  but  can- 
not find  it  when  stationary,  unless  it  is  close  to  his  feet. 

Case  A,  432.  January  11,  1900. — Boy,  aged  2  years 
2  months,  was  brought  to  me  at  West  Ham  Hospital. 
He  had  alternating  convergent  squint  270.  Squinted 
more  in  near  vision.  Mother  said  he  had  squinted  less 
than  a  month.  I  ordered  ung.  atrophias  thrice  daily, 
for  both  eyes,  and  told  the  mother  to  bring  him  again 
in  a  week  to  have  his  eyes  tested  for  glasses. 

November  j,  1901  (one  year  and  ten  months  later). 
— The  mother  did  not  use  the  ointment  and  come 
again  as  directed,  as  the  child's  father  "  did  not  believe 
in  having  the  eyes  messed  about  with."  Child  now 
has  convergent  squint  L.  E.  340.  L.  E.  has  lost  the 
power  of  central  fixation,  and  the  ivory-ball  test  shows 


Case  D,  730.  July  13,  1901. — Girl,  aged  7  weeks, 
has  convergent  squint  R.  E.  io°  approximately,  angle 
varies  slightly.     Good  central  fixation  R.  E. 

July  17. — Retinoscopy  under  atropine,  each  eye  + 
2*5  D  sph.  Ordered,  ung.  atropine  for  L.  E.  only, 
every  morning. 

July  51. — Child  uses  R.  E.  (unatropised)  almost  as 
often  as  L.  E.  (atropised).  Ordered,  continue  atropine 
L.  E.  only. 

August  28. — Atropine  has  not  been  used.  R.  E.  now 
converges  300  about,  fairly  constant  in  degree.  R.  E. 
has  lost  the  power  of  central  fixation.  Ordered,  con- 
tinuous occlusion  L.  E.  for  three  days. 

August  31. — No  fixation  R.  E. 

1  did  not  care  to  order  continuous  occlusion  of  this 


JO  AMBLYOPIA 

very  young  infant's  better  eye  for  many  weeks,  for  fear 
of  rendering  it  amblyopic.  I  therefore  ordered  the  eye 
to  be  bandaged  half  of  each  day.  In  six  weeks  R.  E. 
had  regained  steady  central  fixation. 

Case  B,  24.  February  4,  1896.— I  was  asked  to  see 
a  girl  aged  2  years  10  months.  L.  E.  had  squinted 
occasionally  since  she  had  whooping  cough,  aged  i\ 
years,  but  for  the  last  four  or  five  weeks  the  squint 
had  been  constant.  Angle  of  convergence  260.  After 
instilling  atropine  into  E.  E.  only  for  about  an  hour, 
she  turned  in  R.  E.  and  used  L.  E.  always,  both  in 
near  and  distant  vision.  She  could  easily  see  a  small 
marble  at  the  other  end  of  the  room  with  L.  E.  The 
sight  of  this  L.  E.  must  have  been  perfect  or  nearly  so. 

A  week  later,  retinoscopy  under  atropine. — R.  E.  + 
4-5  D,  L.  E.  4-  5*5  D. 

I  ordered  spectacles  for  constant  wear,  R.  E.  +  4  d 
sph.,  L.  E.  4-  5  U  sph.  I  also  ordered  a  drop  of 
atropine  to  be  put  in  R.  E.  only  every  morning,  and 
proposed  exercises  with  the  amblyoscope  in  a  few 
weeks. 

The  parents,  not  being  favourably  impressed  by  my 
methods,  determined  to  have  "  another  opinion." 
The  child  was  taken  to  an  ophthalmic  surgeon  who 
said  she  was  too  young  for  glasses.  He  ordered  atro- 
pine for  both  eyes  twice  daily.  This  was  kept  up  for 
rather  more  than  a  year,  after  which  she  was  given 
spectacles.  At  the  age  of  7  years  the  surgeon  operated 
on  the  left  eye  (tenotomy). 

December  17,  1901. — The  child  was  brought  to  me 
live  years  and  ten  months  after  1  saw  her  first.  She 
had  convergence  of  L.  E.  14",  while  wearing  her  glasses. 
L.  E.  was  prominent  and  caruncle  sunk.  The  L.  E. 
had  lost  the  power  of  central  fixation,  ami  its  vision 
was  reduced  to  the  counting  of  fingers  at  one  foot  from 
the  face.  1  have  since  removed  the  deformity  by 
advancement  of  the  left  external  rectus,  but  the  eye 
oi  course  remains  hopelessly  blind. 


CONGENITAL    AND    ACQUIRED  7  I 

Case  B,  83.  October  27,  1897.— A  girl,  aged  2  years, 
was  brought  to  me.  The  mother  said  she  had  squinted 
occasionally  for  several  months,  but  she  had  squinted 
constantly  since  a  few  days  before  the  August  bank 
holiday.  She  had  convergent  squint  L.  E.  21°.  Using 
R.  E.  she  could  always  see  the  half-inch  ivory  ball  at 
the  far  end  of  the  (22  feet)  room.  When  R.  E.  was 
bandaged  she  could  see  the  1^  inch  ball  with  the  L.  E., 
but  she  had  great  difficulty  in  finding  the  1  inch  ball 
unless  she  was  allowed  to  begin  to  run  after  it  before 
it  had  stopped  rolling. 

November  1,  1897. — Retinoscopy  under  atropine 
shows  error  of  refraction  to  be,  each  eye  +  3*5  D  sph. 
+  075  D  cyl.  ax.  vert.  Ordered,  spectacles  0*5  D 
less  than  the  retinoscopy  ;  continuous  occlusion  of 
R.  E.  for  seven  days  ;  after  that,  one  drop  of  liquor 
atropinae  to  be  put  into  R.  E.  only  every  morning. 

December  7,  1897. — Child  uses  R.  E.  (atropised)  in 
distant  vision,  and  L.  E.  (unatropised)  in  near  vision. 
Angle  170  with  glasses.     Ordered,  continue. 

February  8,  1898. — Child  now  uses  (unatropised) 
L.  E.  always,  both  in  near  and  distant  vision,  and 
squints  always  with  (atropised)  R.  E.  Ordered,  stop 
using  the  atropine  and  come  again  in  a  month. 

June  29,  1899  (one  year  and  four  months  later). — 
Soon  after  the  last  visit  the  child's  father,  a  bank 
manager,  was  transferred  to  a  post  in  the  north  of 
England.  The  mother  said  that,  as  she  was  not  able 
to  bring  the  child  to  me,  she  thought  she  had  better 
continue  the  drops.  She  used  the  drops,  for  the  R.  E. 
only,  every  day  for  about  six  months.  Not  since. 
The  child  has  now  constant  squint  R.  E.  11°,  with  the 
glasses.  Ivory-ball  test  shows  vision  of  L.  E.  to  be 
perfect,  but  vision  of  R.  E.  is  barely  ^%.  Central  fixa- 
tion is  present  in  R.  E.  but  unsteady. 

Of  course  all  possible  means  have  since  been  used 
to  restore  the  sight  of  the  R.  E.  The  child  has  now 
learnt  to  read.      On  November  8,  1901,  the  vision  of 


72 


AMBLYOPIA 


the  L.  E.  (which  at  first  squinted)  was  |,  and  the 
vision  of  the  R.  E.  (which  was  at  first  the  fixing  eye) 
was  iL. 

Case  D,  332.  On  May  9,  1900,  I  saw,  at  Moorfields, 
a  boy,  aged  3  years  2  months.  He  had  squinted  con- 
stantly, R.  E.,  since  the  age  of  2  years  8  months.  Xo 
heredity.  Abversion  perfect.  C.  S.  R.  E.  460.  Good 
central  fixation  R.  E.  Easily  sees  half-inch  ivory  ball 
at  about  20  feet  with  R.  E.  Ordered,  atropine  both 
eyes  for  retinoscopy. 

May  16,  1900.  —  C.  S.  R.  E.,  with  atropine,  370. 
Retinoscopy  R.  E.  +  7  I)  sph.  +  1-25  D  cyl.  ax.  vert. 
L.  E.  +  6*25  D  sph,  +  1-5  D  cyl.  ax.  vert.  Ordered, 
glasses  o-5  D  less  than  retinoscopy  ;  also,  guttas  atro- 
phias 1  per  cent.  L.  E.  only  every  morning.  To  return 
in  one  month. 

June  5,  1901  (thirteen  months  later).  —  Mother  used 
drops  for  L.  E.  for  a  month,  but  was  then  ill,  so  child 
has  since  been  neglected.  The  glasses  have  been  worn 
constantly.  C.  S.  R.  E.  360.  R.  E.  has  lost  the  power 
of  central  fixation.  Ordered,  continuous  occlusion 
L.  E.  for  one  month. 

July  3,  1901.  —  Central  fixation,  R.  E.,  regained. 
Ordered  guttas  atrophias  1  per  cent.  L.  E.  only  every 
morning  for  two  months. 

August  28,  1901. — Patient  uses  L.  E.  (atropised)  in 
distant  vision,  and  R.  E.  (unatropised)  in  near  vision. 
Ordered,  continue  drops  L.  E.  only,  for  two  months. 

December  4,  1901.  —  Drops  have  been  used  until 
three  weeks  ago,  not  since,  as  they  were  all  finished. 
Child  now,  without  atropine,  uses  the  originally  squint- 
ing R.  E.  always,  and  squints  constantly  with  the 
originally  fixing  L.  E. 

April  2,  [902.  —  Last  time  1  accidentally  omitted  to 
give  the  mother  written  directions  ;  there  w.is,  there- 
fore, some  misunderstanding.  Child  now  squints  con- 
stantly with  L.  E.  (the  originally  fixing  eye)  240.      L.  E 


CONGENITAL    AND    ACQUIRED  J 3 

has  central  fixation,  but  very  unsteady.  Ordered, 
guttae  atrophias  1  per  cent.  R.  E.  only,  every  morning 
for  one  month. 

May  7,  1902. — Child  will  not  use  (unatropised)  L.  E. 
voluntarily  even  in  near  vision.  Ordered,  continuous 
occlusion  R.  E.  for  one  month. 

June  4,  1902.  —  Steady  central  fixation  L.  E. 
Ordered,  discontinue  pad  and  use  guttae  atropinae 
R.  E.  only,  for  two  months. 

August  6,  1902. — Child  now  uses  L.  E.  (unatropised), 
and  squints  with  R.  E.  (atropised),  always  in  near 
vision,  and  usually  in  distant  vision  also.  Ordered, 
stop  drops. 

August  30,  1902. — Child  now  uses  either  eye  in- 
differently, alternating  convergent  squint  240,  with 
glasses. 

Case  D,  286.  October  9,  1900. — Girl,  aged  5  years 
7  months.  She  began  to  squint  suddenly  at  the  age 
of  3  years  9  months,  and  had  squinted  constantly 
ever  since.  Already  under  atropine.  C.  S.  L.  E.,  360. 
Retinoscopy,  R.  E.  +  4-5  D  sph.  +  0*25  D  cyl.  ax. 
horiz.  ;  L.  E.  same  at  approximate  macula.  Fixation 
lost  L.  E.  Ordered  glasses  +  4  D  sph.  each  eye. 
R.  E.  to  be  continuously  occluded  for  one  month. 

August  9,  1 90 1. — Case  has  been  neglected,  except 
that  glasses  have  been  worn.  V.  R.  E.  f,  V.  L.  E.  -^. 
No  fixation  L.  E.  Ordered,  continuous  occlusion  R.  E. 
for  three  weeks. 

August  30,  1901.  —  Treatment  carried  out.  Good 
central  fixation  L.  E.  V.  L.  E.  T%.  Ordered,  guttaa 
atropinae  R.  E.  only,  for  six  weeks. 

October  4,  1901.— V.  L.  E.  f.  C.  S.  160.  Child  uses 
L.  E.  (unatropised)  in  near  vision  and  R.  E.  (atropised) 
in  distant  vision.  Ordered,  continue  atropine  R.  E. 
only,  for  two  months. 

December  3,  1901. — Vision  §  each  eye.  Child  uses 
L.  E.  and  squints  with  R.  E.  always,  both  in  near  and 


74  AMBLYOPIA 

distant  vision.  Ordered,  stop  atropine  and  come  in 
two  weeks. 

May  6,  1902. —  Child  has  not  been  seen  for  live 
months.  She  has  squinted  constantly  with  K.  E.  (the 
originally  fixing  eye)  during  that  time.  V.  R.  E.  T*^, 
V.  L.  E.  f.  Amblyopia  to  ^  acquired  in  R.  E.  since 
last  December.  Ordered,  gutt?e  atropine  L.  E.  only, 
for  one  month. 

June  6,  1902.— Squints  now  with  L.  E.  (atropised) 
1 8°.     V.  §  each  eye. 

NOTE.  —  This  case  is  altogether  exceptional,  on 
account  of  the  age  (nearly  seven  years)  at  which 
amblyopia  in  the  R.  E.  was  acquired. 

Amblyopia  ex  anopsia,  like  congenital  ambly- 
opia, concerns  almost  entirely  the  central  and 
paracentral  region  of  the  retina,  and  produces  no 
contraction  of  the  peripheral  limits  of  the  field 
of  vision.  But  the  blindness  often  reaches  an 
extreme  degree  which  is  never  met  with  in  the 
congenital  form.  In  congenital  amblyopia  the 
central  vision  is  never  lower  than  ^,  the  visual 
acuity  normally  found  at  50  from  the  fixation 
point.  In  an  extreme  case  of  acquired  blind- 
ness, on  the  other  hand,  there  is  often  a  scotoma 
extending  about  250  to  300  round  the  centre  of 
the  field  of  vision.  In  this  scotoma  there  may 
be  bare  perception  of  light.  Outside  this  area 
fingers  may  be  counted  a  foot  or  two  from  the 
face. 

Amblyopia   in    Casks   ok  Convergent   Squint. 

Congenital  and  acquired  amblyopia  having  been 
studied   separately,  one   is   now    in   a  position   to 


CONGENITAL    AND    ACQUIRED  75 

discuss  the  cause  of  the  blindness  so  often  found 
in  cases  of  unilateral  convergent  squint.  In  any 
individual  case,  seen  for  the  first  time  when  the 
squint  has  lasted  several  years,  it  is  impossible 
to  say  how  much  of  the  blindness  may  be  due  to 
disuse  of  the  deviating-  eye,  and  how  much  may 
be  congenital.  Statistics,  however,  enable  one 
to  draw  a  very  accurate  general  conclusion. 

Tables  iii.,  iv.,  and  v.,  show  the  visual  acuity 
of  the  deviating  eye  in  cases  of  constant  uni- 
lateral convergent  squint.  I  used  Snellen's  types 
or  the  ivory-ball  test  at  the  first  visit,  when 
possible,  and  on  many  subsequent  occasions. 
Nearly  all  these  children  have  since  become  old 
enough  to  allow  me  to  confirm  the  results  of 
the  ivory-ball  test  by  Snellen's  types.  The 
visual  acuity  noted  in  the  tables  is  the  final 
result,  with  optical  correction,  and  after  all 
possible  means  had  been  used  to  remove  any 
acquired  amblyopia. 

I  have  included  in  the  tables  only  cases  in 
which  I  could  be  reasonably  certain  as  to  the 
time  of  onset  of  the  deviation,  and  in  which 
my  directions  were  subsequently  followed  to 
my  satisfaction.  The  cases  had  either  received 
no  treatment  before  I  first  saw  them,  or  they 
had  merely  been  given  glasses.  Some  had 
been  operated  upon. 

Any  defect  of  vision  found  in  the  cases  in 
table   iii.    may  be   considered  as    congenital.      In 


76 


AMBLYOPIA 


these  recent  cases,  any  amblyopia  which  might 
have  been  acquired  would  certainly  have  been 
removed  by  the  subsequent  treatment. 

Table  iv.  shows  the  visual  acuity  of  the  deviat- 
ing" eye  after  all  possible  means  had  been  used 
to  remove  any  defect  which  might  be  present. 
The  vision  was  at  first,  in  many  cases,  very 
considerably  lower  than  shown  in  the  tables. 

In  the  cases  in  table  v.  the  squint  had,  in 
most  cases,  lasted  so  long  that  no  improvement 
in  vision  was  possible. 

A  comparison  of  table  iii.  with  table  v.  shows 
that  congenital  amblyopia  only  occurs  in  a  very 
small  proportion  of  the  cases,  and  is  never  re- 
sponsible for  the  extreme  blindness  so  often 
found  in  neglected  cases  of  unilateral  squint. 


Tables  Showing  the  Visual  Acuity  of  the  Deviating 
Eye  in  787  Cases  of  Constant  Unilateral  Con- 
vergent Squint. 

Table  III. 

Cases  which  I  saw  first  when  the  patient  had  squinted  during 
less  than  one-eighth  of  his  or  her  life. 


Vision  of  the 
deviating  eye. 

Age  ol  0 

lset  of  the  deviation. 

Before 
12  months. 

1  to  3  yrs. 

After  3  yrs. 

Total. 

i 

33 

62 

80 

165 

f  and  A 

2 

6 

9 

17 

T6g  and  q^ 

1 

3 

5 

9 

368  and  B6a 

0 

1 

1 

2 

Less  than  g'V 

0 

0 

0 

0 

Fixation  lost 

0 

0 

O 

0 

irrecoverably 

CONGENITAL    AND    ACQUIRED 


7 


Table  IV. 

Cases  which   I  saw  first  when  the  patient  had  squinted  during 
more  than  one-eighth  and  less  than  on?-half  of  his  or  her  life. 


Vision  of  the 
deviating  eye. 


f  and  T% 

^g  and  56¥ 

B<V  and  v% 

Less  than  %% 

Fixation    lost 

irrecoverably 


Age  of  onset  of  the  deviation. 


Before 

.  i    o  •?  yrs. 

12  months. 


After  3  yrs. 


Total. 


Table  V. 

Cases  which  I  saw  first  when  the  patient  had  squinted  dnrin> 
more  than  one-half  of  his  or  her  life. 


Vision  of  the 
deviating  eye. 

Age  of  onset  of  the  deviation. 

Before 
12  months. 

i  to  3  yrs. 

After  3  >rs. 

Total. 

'i 

f  and  ^V 

Te8  and  & 

36  and  e6o 

Less  than  e6s 

Fixation    lost 

irrecoverably 

o 

2 

4 
8 

55 
56 

3 

7 

32 

53 
103 
1 10 

11 

19 
54 
4i 

25 

14 
28 
90 
102 
179 
191 

When  I  have  been  consulted  about  a  case  of  squint,  I 
have  always  warned  the  parents  of  the  patient  that,  in  the 
event  of  a  younger  member  of  the  family  developing  a 
squint,  the  case  ought  to  receive  attention  without  delay. 
I  have,  therefore,  been  fortunate  enough  to  see  an  unusually 
large  proportion  of  my  cases  soon  after  the  first  appearance 
of  the  deviation. 

It  is  remarkable  that  only  eight  cases,  commencing 
before  twelve  months  of  age,  appear  in  table  iv.  This  is 
evidently  because  parents  who  have  been  warned,  and 
those  who  are  especially  solicitous  for  the  welfare  of  their 
children,  seek  advice  immediately.  These  cases  are  included 
in  table  iii.  The  other  infants  are  usually  left  without 
treatment  for  several  months,  so  that  they  appear  in  table  v. 


7§ 


CHAPTER    VI. 

THE    METHOD    OF    INVESTIGATING    A    CASE    OF 
SQUINT. 

Every  case  of  squint  should  be  systematically 
investigated,  as  it  is  only  by  a  thorough  knowledge 
of  each  case  that  a  rational  line  of  treatment  can 
be  determined  upon.  The  following  is  the  plan 
I  always  use.  It  may  appear  rather  formidable 
at  first  sight,  but,  with  practice,  one  can  carry  out 
the  various  tests  with  great  rapidity  and  precision. 
The  time  will  surely  not  be  grudged  when  it  is 
remembered  that,  in  cases  which  are  presented 
early  enough,  the  patient's  whole  future  career 
may  depend  upon  the  skill  and  care  of  the  surgeon 
who  first  sees  the  case. 

(i)  History. 

(2)  The  character  of  the  squint 

(3)  The  power  of  fixation  in  the  deviating  eye. 

(4)  Movements  of  each  eye  separately.  Dyna- 
mic convergence. 

(5)  Vision  testing. 

(6)  The  condition  of  the  fusion  faculty. 

(7)  The  angle  of  the  deviation. 


INVESTIGATION    OF    SQUINT  79 

After  using  atropine  for  from  three  to  eight 
days : — 

(8)  The  refraction. 

(1)  History. — Under  this  head  should  be 
noted  :  (a)  Age  of  onset,  when  it  can  be  deter- 
mined. It  may  often  be  fixed  very  precisely  by 
reference  to  some  family  event,  such  as  the  birth 
of  the  next  child,  (b)  Mode  of  onset.  Whether 
it  began  as  an  occasional  squint  or  was  constant 
from  the  first,  (c)  Any  illness  or  injury  imme- 
diately preceding  the  appearance  of  the  deviation 
e.g.,  whooping  cough,  measles,  a  blow  on  the 
head,  "fits,"  severe  fright,  &c.  (d)  Evidence 
of  heredity — squint  in  brother,  sister,  or  parents 
of  the  patient. 

(2)  The  Character  of  the  Squint. — The 
presence  of  a  deviation  and  its  character,  whether 
convergent  or  divergent,  unilateral  or  alternat- 
ing, may  often  be  determined  by  simple  inspec- 
tion. But  appearances  are  sometimes  misleading, 
e.g.,  the  high  angle  gamma  often  found  in  hyper- 
metropes  may  simulate  a  divergent  squint  or 
mask  a  slight  convergent  squint.  The  low,  or 
even  negative,  angle  gamma  usually  associated 
with  myopia  may  give  an  appearance  of  abnormal 
convergence  or  mask  a  slight  divergence. 

The  cover  test  is  at  best  only  a  rough  test  having 
many  sources  of  error.  It  is,  moreover,  not  possible 
to  use  it  with  young  children.  Hut,  as  it  is  very 
generally    employed,    it    will    be   well    to    describe  the 


8o  INVESTIGATION    OF    SQUINT 

proper  method  of  making  the  test,  and  the  fallacies  to 
be  guarded  against. 

Tell  the  patient  to  look  steadily  at  some  distant 
object.  Take  a  narrow  card  or  folded  paper  and,  with 
a  rapid  lateral  movement,  cover,  say,  the  patient's  left 
eye,  taking  care  not  to  touch  his  face.  If  the  right 
eye  makes  no  movement  it  was  probably1  not  squinting. 
Now  uncover  the  left  eye,  and  see  that  the  patient 
looks  steadily  at  the  distant  object.  Screen  the 
patient's  right  eye  in  the  same  way.  If  the  left  eye 
makes  no  movement  it  was  probably1  not  squinting 
either.  If,  however,  when  one  eye  is  covered,  the 
other  has  to  make  an  outward  movement  in  order  to 
fix  the  object,  it  was  previously  squinting  inwards  ;  if 
it  rotates  inwards  it  was  squinting  outwards. 

In  a  case  in  which  the  patient  has  been  shown  to 
have  a  squint,  but  in  which  he  can  fix  with  either  eye 
at  pleasure  without  the  other  eye  being  screened,  and 
can  maintain  fixation  after  a  momentary  closure  of  the 
lids,  the  squint  is  alternating. 

In  some  occasional  squints  and  heterophorias,  while 
both  eyes  fix  truly  when  uncovered,  either  eye  deviates 
when  screened,  but  immediately  recovers  itself  on 
removal  of  the  screen. 

The  mirror  lest. — This  is  an  entirely  satisfac- 
tory test,  and  can  be  used  quite  well  even  in  the 
case  of  the  youngest  infants.  The  patient  should 
be  in  the  dark  room,  with  the  lamp  behind  him. 
The  light  is  reflected  from  the  mirror  of  an 
ophthalmoscope,  from  a  distance  of  about  2  ft.,  into 
the  patient's  eyes.  An  infant  will  immediately 
look  at  the   mirror  ;  an  older  patient   should   be 


1  If  the  eye  has  lost  the  power  of  central  fixation,  it  may 
perhaps  make  no  movement,  or  it  may  move  in  a  direction 
which  would  mislead  any  but  a  careful  observer. 


INVESTIGATION    OF    SOUINT  8  I 

told  to  do  so.  A  tiny  image  of  the  ophthal- 
moscope mirror  is  formed  on  the  patient's  cornea. 
Owing-  to  the  angle  gamma,  this  reflection  of  the 
mirror  is  usually  slightly  to  the  nasal  side  of  the 
centre  of  the  pupil.  By  flashing  the  light  rapidly 
from  one  eye  to  the  other,  any  want  of  symmetry 
in  the  position  of  the  reflections  is  at  once 
detected.  It  may  easily  be  seen,  too,  which  is 
the  deviating  eye,  and,  with  practice,  a  very  good 
guess  as  to  the  extent  of  the  deviation  may  be 
made.1 

Squint  or  paralysis. — In  the  case  of  a  patient 
who  is  old  enough  to  speak,  the  persistent  diplopia 
would  prevent  one  mistaking'  a  case  of  paralysis 
of  one  or  more  of  the  external  ocular  muscles 
for  a  case  of  comitant  squint. 

But,  in  the  case  of  an  infant  who  has  recently 
suffered  from  diphtheria,  an  objective  test  is 
required.  The  patient  is  on  the  nurse's  knee  in 
the  dark  room,  with  the  light  behind  him.  The 
nurse  holds  his  head  immovable.  The  light  is 
thrown  into  his  eyes,  from  an  ophthalmoscope 
mirror,  from  a  position  slightly  to  one  side  of 
him.      When  he  fixes  the  mirror  the  approximate 


1  According  to  Hirschberg,  when  the  reflection  on  the 
squinting  eye  is  at  the  margin  of  the  cornea  the  angle  of 
the  deviation  is  about  450,  when  it  is  at  the  margin  of  an 
average-sized  pupil  the  angle  is  about  150.  Allowance 
should  be  made  for  the  estimated  size  of  the  angle 
gamma. 


82  INVESTIGATION    OF    SQUINT 

degree  of  his  deviation  is  noted.  The  light  is 
next  thrown  into  his  eyes  from  the  other  side. 
If,  when  he  again  fixes  the  mirror,  the  angle  of 
the  deviation  is  greater  or  less,  we  have  to  deal 
with  a  paralysis  or  paresis,  and  not  with  a 
comitant  squint. 

In  carrying  out  the  test,  it  is  essential  that  the 
light  be  thrown  into  the  eyes  in  both  cases  from 
approximately  the  same  level,  as,  in  many  cases 
of  true  squint,  the  eyes  converge  more  on  looking 
down  and  diverge  more  on  looking  up. 

(3)  The  Power  of  Central  Fixation. — An 
exceedingly  important  point,  in  its  bearing  on  the 
treatment  and  prognosis  of  a  case  of  unilateral 
squint,  is  the  presence  or  absence  of  the  power 
of  central  fixation  in  the  deviating  eye. 

The  patient  being  in  the  dark  room,  with  the 
light  behind  him,  throw  the  light  from  an  ophthal- 
moscope mirror  first  into  his  good  eye,  while  he 
looks  at  the  mirror.  Note  the  position  of  the 
reflection  of  the  mirror  on  the  cornea  of  this  eye. 
Then  cover  the  good  eye,  and  note  whether  the 
previously  deviating  eye  can  now  fix  the  mirror 
so  as  to  bring  the  corneal  reflection  into  a  corre- 
sponding position.  If  it  does  so,  there  is  central 
fixation.  There  may  be  no  fixation,  in  which 
case  the  eye  wanders.  Or  there  may  be  false 
fixation,  in  which  case  an  eccentric  part  of  the 
retina  is  used  for  the  purpose.  An  eye  which  at 
first    appears    to    have    lost    fixation    may    some- 


INVESTIGATION    OF    SQUINT  S3 

times,    with  a  little   patience,    be   induced    to   fix 

correctly. 

In  the  clinics  one  frequently  sees  some  such  proce- 
dure as  the  following  :  The  surgeon  covers  the  patient's 
good  eye,  then  asks  him  to  follow  the  movement  of  his 
ringer  with  the  deviating  eye.  If  he  is  able  to  do  so, 
it  is  assumed  that  he  has  central  fixation  in  this  eye. 
This  is  entirely  fallacious.  If  the  deviating  eye  has 
any  sight  at  all  it  can  usually  follow  the  movements 
of  a  large  object.  If  the  deviating  eye  has  false 
fixation  in  a  position  of  only  slight  convergence,  even 
the  most  prolonged  examination  by  this  method  will 
certainly  lead  to  error. 

(4)  The  Movements  of  each  Eye  Separately 
should  be  tested  by  covering-  one  eye  and  getting 
the  patient  to  look  with  the  uncovered  eye  from 
side  to  side  and  up  and  down.  The  test  is  then 
repeated  with  the  other  eye.  This  may  usually 
be  done  even  in  the  case  of  young  infants  by 
showing  them  something  in  which  they  are  likely 
to  take  an  interest.  If  each  eye  can  be  separately 
abverted  until  the  edge  of  the  cornea  touches  the 
outer  canthus,  abversion  may  be  considered  full. 
The  power  of  adversion  varies  considerably  within 
normal  limits,  Most  people  can  advert  each  eye 
separately  until  the  corneal  margin  is  within  less 
than  one-tenth  of  an  inch  of  the  caruncle. 

Dynamic  Convergence. — A  careful  distinction 
should  be  made  between  static  and  dynamic  con- 
vero-ence,  iust  as  static  and  dynamic  refraction  are 
distinguished  from  each  other. 


84  INVESTIGATION    OF    SQUINT 

When  a  person  looks  at  a  distant  object,  if  he 
has  no  squint  the  static  convergence  of  the  eyes 
is  nil.  If  he  has  a  convergent  squint  there  is  a 
static  convergence  corresponding  to  the  angle  of 
the  squint.  If  he  has  a  divergent  squint,  the 
static  convergence  is  a  negative  quantity. 

If  now  he  fixes  a  near  object,  there  is  superadded 
to  the  static  convergence  a  dynamic  convergence. 

A  person  who  in  distant  vision  has  no  squint, 
will  usually  exercise  just  sufficient  dynamic  con- 
vergence in  near  vision  (in  association  with  dynamic 
refraction,  or  accommodation)  to  allow  him  to  fix 
the  object  correctly  with  both  eyes.  If,  however, 
his  dynamic  convergence  be  excessive,  the  eyes 
will  tend  to  squint  inwards  in  near  vision.  A 
perfect  fusion-sense  will  keep  this  tendency  in 
check.  But  if  the  fusion-sense  be  defective,  this 
tendency  will  be  free  to  cause  a  squint  in  near 
vision.  In  a  case  of  divergent  squint,  when  the 
fixing  eye  accommodates  for  a  near  object  the 
divergent  eye  will  usually  recover  itself  to  a 
certain  extent.  In  convergent  squint,  the  faulty 
eye  should  turn  in  still  more  towards  the  nose 
in  near  vision.  As  will  be  seen  later,  the  esti- 
mation of  the  dynamic  convergence  is  of  the 
utmost  importance  in  deciding  the;  question  of 
operation  for  squint.   / 

Method  of  climating  the  dynamic  convergence 
in  a  case  of  squint.  -Stand  at  arm's  length 
from  the    patient.       Shut  one    eye  and  hold  the 


INVESTIGATION    OF    SQUINT  85 

point  of  the  finger,  or  perhaps  some  more 
attractive  object,  in  line  with  the  open  eye  and 
the  patient's  fixing  eye.  Let  the  patient  look  at 
the  object  while  it  is  gradually  brought  nearer 
his  fixing  eye.  The  fixing  eye  will  remain 
immobile,  the  deviating  eye  manifesting  the  con- 
vergence of  both.  In  this  way,  the  slightest 
movement  of  convergence  of  the  deviating  eye 
can  at  once  be  seen,  and  the  point  at  which  the 
deviating  eye  begins  to  diverge  again  can  be 
accurately  noted.  This  simple  procedure  should 
never  be  omitted. 

(5)  Vision  Testing. — (a)  The  vision  of  patients 
who  are  old  enough  to  read  letters  should  be 
tested  with  Snellen's  distant  types.  This  would 
appear  a  very  simple  matter,  yet  it  is  surprising- 
how  often,  in  the  clinics,  one  finds  the  vision  of 
the  better  eye  recorded  as  the  vision  of  each  eye, 
even  by  experienced  assistants.  The  desire  to 
use  the  accustomed  eye  is  so  strong  that,  when 
this  is  shaded,  the  patient  will  involuntarily  screw 
his  head  round  to  try  to  see  past  the  shade. 

{b)  Ivory-ball  test  for  young-  children. — Apart 
from  its  scientific  interest,  it  is  often  of  great 
practical  importance  to  be  able  to  estimate  approxi- 
mately a  young  child's  visual  acuity.  For  this 
purpose  I  use  five  little  ivory  balls  varying  in  size 
from  half  an  inch  to  one  and  a  half  inches  in 
diameter.  The  child  is  first  allowed  to  handle  the 
balls  with  both  eyes  open.  Then  one  eye  is  covered 
7 


86  INVESTIGATION    OF    SQUINT 

by  a  pad,  or,  if,  he  wears  glasses,  by  a  piece  of  cotton 
wool  stuffed  behind  the  lens.  He  is  then  asked 
to  go  and  pick  up  the  balls  as  they  are  thrown  on 
the  floor  to  a  distance  of  six  or  seven  yards,  one 
by  one,  beginning  with  the  largest.  By  spinning 
the  ball  in  the  fingers  as  it  is  thrown,  it  can  be 
made  to  "break"  on  touching  the  floor,  so  that  it 
does  not  go  quite  in  the  direction  in  which  it 
appeared  to  have  been  thrown.  It  is  easy  to  tell, 
by  the  way  in  which  the  child  runs  for  the  ball, 
whether  he  really  sees  it  before  he  starts  or  is  only 
going  to  look  for  it.  I  test  the  presumably  better 
eye  first,  so  as  to  give  the  other  eye  the  benefit  of 
experience. 

Children  are  always  ready  to  play  this  ball 
game.  This  method  of  vision-testing  only  takes 
a  few  minutes,  and  it  succeeds  with  most  children 
who  are  old  enough  to  walk.  I  have  used  it  since 
1896,  and,  in  cases  in  which  I  have  subsequently 
been  able  to  test  the  vision  by  means  of  Snellen's 
types,  I  have  found  my  conclusions  confirmed. 

(6)  The  Condition  of  the  Fusion  Faculty 
may,  as  a  matter  of  convenience,  be  investigated 
at  this  point,  but  it  is  usually  better  to  defer  the 
examination  until  the  state  of  the  refraction  has 
been  ascertained  and  the  effect  of  the  mydriatic 
has  passed  off. 

Examination  with  the  amblyoscope  I  have  found 
by  far  the  most  rapid,  precise,  and  reliable  method 
of  ascertaining  the  condition  of  the  fusion  sense. 


INVESTIGATION    OF    SQUINT  87 

Of  late  years  I  have  used  it  to  the  exclusion 
of  all  other  methods.  It  is  fully  described  in 
chapter  viii. 

I  wish  again  to  draw  attention  to  the  distinc- 
tion between  the  possession  of  the  fusion  faculty 
and  the  presence  of  binocular  vision.  A  patient 
may  have  a  convergent  squint  of  very  high 
degree,  with  suppression  of  the  vision  of  the 
deviating  eye,  and  yet  training  with  the  amblyo- 
scope  may  have  perfectly  developed  his  fusion 
faculty.  In  this  case,  if  the  patient  looks  into 
the  amblyoscope  while  the  instrument  is  adapted 
to  the  angle  of  the  squint,  he  fuses  the  pictures 
— his  fusion  faculty  finds  its  expression  in  the  act 
of  binocular  vision.  The  same  thing  happens 
when  his  eyes  are  put  approximately  "straight" 
by  operative  or  other  means. 

Javal,  Maddox,  and  others  estimate  the  "  depth  of 
suppression "  by  the  ease  or  difficulty  with  which 
diplopia  may  be  artificially  elicited.  Diplopia  may 
sometimes  be  elicited  by  placing  a  red  glass  before 
the  better  eye  and  alternately  covering  and  uncover- 
ing it  while  the  patient  looks  at  a  candle  flame.  There 
is  a  fallacy  here  which  must  be  guarded  against — the 
patient  recognises  the  fact  that  he  sees  a  red  light 
with  the  "good"  eye,  and  that,  when  this  is  covered, 
he  sees  a  white  light.  He  therefore  often  says  he  sees 
two  lights,  a  red  and  a  white,  even  though  he  does  not 
see  them  both  simultaneously.  If  the  red  glass  fails 
to  produce  diplopia,  success  may  often  be  attained  by 
placing  a  horizontal  prism  before  the  deviating  eye,  so 
as  to  throw  the  image  of  the  flame  on  a  part  of  the 
retina  nearer  the  macula. 


88  INVESTIGATION    OF    SQUINT 

Some  writers  have  recommended,  as  a  test,  placing 
a  prism  vertically  before  one  eye,  to  throw  the  false 
image  out  of  what  they  call  the  "  band  of  suppression." 
Diplopia  can  almost  always  be  elicited  in  this  way, 
even  in  cases  of  total  absence  of  the  fusion  sense. 
The  explanation  of  this  is  not  far  to  seek.  The  con- 
jugation of  the  two  eyes  in  horizontal  movements, 
being  intended  to  subserve  the  act  of  binocular  vision, 
was  probably  acquired  at  no  very  early  period  in  the 
development  of  the  human  race.  The  conjugation  of 
the  eyes  in  vertical  movements,  on  the  other  hand,  I 
believe  we  share  to  a  great  extent  with  most  of  the 
mammals.  It  is  not  surprising  that  disturbance  of 
this  very  ancient  function,  by  vertical  displacement 
of  the  image  in  one  eye,  should  produce  diplopia. 

But  diplopia  tests  really  give  very  little  information 
as  to  the  condition  of  the  fusion  sense.  Some  cases, 
in  which  diplopia  is  with  difficulty  elicited  by  these 
methods,  readily  get  the  highest  grade  of  binocular 
vision  after  fusion  training  with  the  amblyoscope,  and 
are  subsequently  completely  cured.  Others,  again, 
who  easily  see  double,  may  be  incapable  of  acquiring 
more  than  grade  i  binocular  vision. 

7)  The  Measurement  of  the  Angle  of 
the  Deviation. — At  the  first,  and  at  each  sub- 
sequent visit,  the  angle  of  the  deviation  is 
accurately  measured.  When  the  child  has  been 
ordered  glasses,  the  measurement  is  always  made 
with  the  glasses  on.  The  case-sheet  then  shows 
at  a  glance  the  progressive  effect  of  the  treat- 
ment upon  the  deviation,  and  helps  one  to  decide 
whether  it  is  advisable  to  supplement  this  treat- 
ment by  operation. 

Four  methods  of  measuring  the  angle  of  devia- 
tion are  here  described. 


INVESTIGATION    OF    SQUINT  89 

(a)  The  deviometer} — This  instrument  can  be 
very  rapidly  used,  no  adjustment  being  required. 
Measurements  obtained  by  it  are  very  accurate. 
It  can  be  used  quite  easily  even  with  the  youngest 
children. 

A  wooden  stand,  about  10  inches  high,  supports 
a  horizontal  wooden  arm,  2  inches  wide,  \  inch 
thick,  and  about  2  feet  long.  This  arm  is 
pivoted  at  the  end,  so  that  it  may  be  swung 
over  to  either  side  as  required.  The  arm  is 
painted  black  in  front.  On  the  back  is  a 
scale  of  tangents  to  degrees  at  60  centimetres 
distance.  A  flat,  hook-shaped  piece  of  brass, 
having  a  white  spot  on  it,  slides  along  the  arm. 
In  front  of  the  pillar,  below  the  zero  of  the  scale, 
is  a  specially  made  electric  lamp,  5  inches  high 
and  f  inch  in  diameter.  Flexible  wires  go  from 
the  electric  lamp  to  the  wall  plug.  An  electric 
bell-push  is  used  instead  of  a  switch,  so  that,  by 
pressing  the  button,  the  light  may  be  flashed  on 
and  off  very  rapidly.  A  string  60  centimetres 
long  is  attached  to  the  upright  pillar  of  the  instru- 
ment.    At  the  end  of  the  string  is  a  ring. 

Measurements   and  details   of   construction  of 
the  deviometer  will  be  found  in  the  appendix. 
The  instrument  is  put  on  a  table.     The  nurse 


1  I  have  no  wish  to  claim  originality  for  this  instrument. 
The  principle  is  that  of  Maddox'  scale  and  Priestley 
Smith's  tape,  the  former  of  which  I  used  for  years  before 
I  devised  the  deviometer. 


go 


INVESTIGATION    OF    SQUINT 


sits  at  the  table  with  the  child  on  her  knees.  She 
puts  the  ring  on  her  finger,  and  holds  the  child's 
head  steady  with  her  hands,  keeping  the  string 
taut.  The  surgeon  "sights"  the  child's  eyes 
through   the   nick  in   the  top  of  the  stand,  and 


Fig.  9. 

presses  the  button.  The  child  immediately  looks 
at  the  light  with  his  fixing  eye.  The  reflection 
of  the  lamp  forms  a  vertical  line  of  light  on  the 
cornea  of  this  eye,  which  shows  the  correct 
position  of  fixation.  The  position  of  the  line  of 
light  on  the  cornea  of  the  squinting  eye  enables 
a  good  guess  to  be  made  as  to  the  angle  of  the 
deviation.     The  light  is  discontinued.     The  brass 


INVESTIGATION    OF    SQUINT  9 1 

traveller  with  the  white  disc  is  slid  along  the  arm 
to  the  position  which  corresponds  to  the  guess. 
The  brass  traveller  being  tapped  with  the  finger, 
the  metallic  sound  causes  the  child  to  look  at  it. 
If  it  does  not,  a  lighted  match,  held  in  front  of 
the  traveller,  will  always  attract  his  attention. 
The  button  is  then  pressed,  and  the  light  flashed 
on  for  an  instant.  If  the  line  of  light  on  the 
cornea  of  the  squinting  eye  is  in  a  corresponding 
position  to  that  which  it  formerly  occupied  in  the 
fixing  eye,  the  angle  of  the  squint  is  read  off  on 
the  scale  on  the  back  of  the  arm.  If  not,  the 
traveller  is  moved  a  little,  and  when  the  child 
looks  at  it  the  light  is  flashed  on  again,  and  so 
on  till  the  true  position  is  found. 

An  older  patient  can,  of  course,  sit  at  the  table 
and  hold  the  string  himself,  and  look  at  the  zero 
of  the  scale,  or  the  white  disc  on  the  traveller, 
when  directed  to  do  so. 

(b)  Maddox  tangent  scale  (fig.  20,  page  171)  is 
an  admirable  device  for  measuring  the  deviation. 
The  method  is  very  rapid  and  accurate.  It  is 
not,  however,  easy  to  use  with  small  children.  I 
always  use  it  at  Moorfields,  because  the  apparatus 
is  fixed  in  the  wall  out  of  harm's  way,  and  there 
is  nothing  to  get  out  of  order,  however  roughly  it 
may  be  used. 

The  large  figures  are  used  for  measuring 
heterophorias  with  the  Maddox  rod.  With  these 
we  are    not  at    present    concerned.      The  small 


Q2  INVESTIGATION    OF    SQUINT 

figures,  in  the  horizontal  scale,  represent  tangents 
to  degrees  at  a  distance  of  one  metre.  They  are 
printed  on  a  strip  of  paper,  which  is  pasted  on 
a  board  about  seven  feet  long.  In  the  centre 
of  this  scale  is  a  candle.  Below  the  candle  is 
attached  a  light  bamboo  rod  one  metre  long. 

The  patient  rests  his  cheek  against  the  end  of 
the  metre  rod.  The  surgeon  puts  his  head  below 
the  rod,  so  that  his  eye  is  vertically  below  the 
rays  of  light  which  pass  from  the  candle  to  the 
patient's  face.  The  patient  is  first  told  to  look 
at  the  light.  The  position  of  the  image  of  the 
candle  flame  on  the  cornea  of  the  fixing  eye  is 
noted.  A  guess  is  made  as  to  the  angle  of  the 
squint.  The  patient  now  is  told  to  look  at  the 
figure  which  represents  the  guess.  If  this  is  too 
much  or  too  little,  other  figures  are  named  till 
the  reflection  of  the  candle  flame  on  the  cornea 
of  the  deviating  eye  occupies  a  position  similar 
to  that  which  it  formerly  occupied  in  the  fixing 
eye. 

(c)  Priestley  SmitJi  s  tape  method. — The  advan- 
tages of  this  method  are  that  it  takes  very  little 
time  and  the  apparatus  required  is  simple.  It  is 
moderately  accurate.  It  is,  however,  not  easy  to 
use  with  young  children. 

A  string  one  metre  long  has  a  ring  at  one  end. 
To  the  ring  is  attached  a  graduated  tape.  The 
tape  has  a  weight  at  its  other  end.  The  patient 
holds  the  free  end  of  the  string  against  his  temple. 


INVESTIGATION    OF    SQUINT  93 

The  surgeon  puts  the  ring  on  a  finger  of  one  of 
his  hands  in  which  he  holds  an  ophthalmoscope 
mirror.  The  tape  is  allowed  to  slide  between  the 
fingers  of  the  other  hand,  the  weight  keeping  the 
tape  taut.  The  patient  is  first  told  to  fix  the 
mirror,  while  the  light  of  a  lamp  is  reflected  into 
the  fixing  eye.  The  position  of  the  image  of  the 
mirror,  on  the  cornea  of  the  fixing  eye,  is  noted. 
The  light  from  the  mirror  is  now  thrown  on  to 
the  deviating  eye,  and  the  patient  is  directed  to 
look  at  the  surgeon's  tape  hand.  This  is  moved 
horizontally,  till  the  position  of  the  image  of  the 
mirror,  on  the  cornea  of  the  squinting  eye,  is 
similar  to  that  which  it  formerly  occupied  on  the 
cornea  of  the  fixing  eye.  The  string  keeps  the 
ophthalmoscope  hand  at  one  metre  from  the 
patient's  eye.  The  observer  keeps  the  tape  hand 
as  nearly  as  possible  at  the  same  distance  from 
the  patient's  eye.  The  graduated  scale  on  the 
tape,  where  it  slides  through  the  tape  hand,  shows 
approximately  the  angle  of  the  deviation  in  degrees. 

If  the  length  of  the  string  be  made  60  cm.  instead 
of  one  metre,  an  ordinary  Continental  tape  measure 
may  be  used  for  the  graduated  tape,  one  centimetre 
representing  approximately  one  degree. 

(d)  The  perimeter  method. — I  describe  this 
because  a  perimeter  is  to  be  found  in  every  eye 
clinic  and  ophthalmic  surgeon's  consulting  room. 
The  patient  is  seated  at  the  perimeter,  which  is 
adjusted  so  as  to  bring  his  deviating  eye  accurately 


94  INVESTIGATION    OF    SQUINT 

in  centre  of  the  arc.  A  candle  is  placed  at  the  far 
end  of  the  room,  in  line  with  the  zero  of  the  peri- 
meter and  the  patient's  deviating  eye.  He  is  told 
to  look  steadily  at  this  candle  with  his  fixing  eye. 
A  second  candle  or  taper,  with  the  eye  of  the 
surgeon  looking  exactly  over  the  top  of  the  flame, 
is  carried  round  the  arc  of  the  perimeter  till  the 
reflection  of  the  flame  lies  in  the  centre  of  the 
cornea  of  the  deviating  eye.  The  position  of  the 
taper  on  the  graduated  arc  of  the  perimeter, 
shows  the  angle  of  the  squint  in  degrees. 

This  is  a  wretched  method.  It  is  inaccurate, 
as  it  takes  no  account  of  the  angle  gamma.  It 
cannot  be  used  in  the  case  of  a  small  deviation, 
as  the  surgeon's  head  then  prevents  the  fixing  eye 
seeing"  the  distant  candle.  It  cannot  be  used  for 
young  children.  The  preliminary  arrangement 
takes  up  so  much  time  that  a  surgeon  who  relies 
upon  this  method  is  apt  to  neglect  to  measure  the 
squint  at  all. 

The  angle  gamma  may  be  measured  separately,  if 
the  patient's  squinting  eye  has  not  lost  the  power  of 
central  fixation.  Cover  the  fixing  eye.  Let  the 
patient  steadily  C\x  the  zero  of  the  perimeter  with  the 
squinting  eye.  The  taper  with  the  surgeon's  eye 
looking  exactly  over  it,  is  carried  along  the  arc  till  the 
reflection  of  the  flame  appears  in  the  centre  of  the 
cornea.  The  position  of  the  taper  on  the  graduated 
arc  shows  the  size  of  the  angle  gamma.  This  angle 
gamma  should  be  added  to  the  perimeter  measurement 
of  a  convergent  squint  and  subtracted  from  that  of  a 
divergent  squint. 


INVESTIGATION    OF    SQUINT  95 

(8)  The  Refraction. — This  is  examined  by 
retinoscopy,  after  atropine  has  been  used,  for  both 
eyes,  three  times  a  day,  for  from  three  to  eight 
days.  For  young  children  I  prefer  the  atropine 
ointment,  i  per  cent.  Atropine  drops,  if  used  too 
freely,  occasionally  cause  unpleasant  symptoms, 
whereas  the  ointment  almost  never  causes  trouble. 
The  nurse  or  mother  should  be  shown  how  to 
insert  the  ointment  within  the  lower  eyelid  with  a 
glass  rod.  One  now  and  then  sees  a  young  child 
in  whom  atropine  produces  perfect  cycloplegia 
with  only  very  slight  mydriasis. 

Children  of  two  years  and  upwards  may,  with  a 
little  tact,  usually  be  induced  to  allow  one  to  put 
on  a  trial  frame  and  proceed  with  retinoscopy  in 
the  usual  way. 

In  the  case  of  a  very  young  child,  a  different 
plan  must  be  followed.  The  nurse  sits  in  the 
dark  room  with  the  child  in  her  arms.  The  light 
is  placed  above  and  behind  the  child's  head.  The 
light  being  reflected  from  the  ophthalmoscope 
mirror  into  the  child's  fixing  eye,  he  immediately 
looks  at  the  mirror.  The  lenses  are  handed,  one 
by  one,  to  the  nurse,  who  holds  them  up  before 
the  fixing  eye,  or  the  surgeon  may  hold  the  lenses 
himself.  There  is  seldom  much  difficulty  so  far. 
Now,  in  order  to  investigate  the  deviating  eye,  it 
is  necessary  to  screen  the  fixing  eye.  The  child 
may,  perhaps,  not  tolerate  any  screen  held  near 
his  face.      In  this  case,  I  hold  a  black  cardboard 


Q6  INVESTIGATION    OF    SQUINT 

screen,  about  halfway  between  the  child's  face  and 
my  own,  in  such  a  way  as  to  cut  off  the  view  of 
the  mirror  from  the  child's  fixing  eye.  The  light 
now  being  thrown  into  the  deviating  eye,  the 
child  looks  at  the  mirror  with  this  eye.  If 
central  fixation  in  the  deviating  eye  of  one  of 
these  very  young  children  has  already  been  lost, 
one  can  only  make  an  approximate  guess  as  to 
the  refractive  error  of  this  eye.  A  glass  may 
then  be  ordered  provisionally,  to  be  exchanged 
for  an  accurate  correction  when  one  has  succeeded 
in  restoring  central  fixation. 

In  the  case  of  an  older  patient,  one  can  measure 
very  accurately  the  refractive  error  of  an  eye  which 
has  lost  fixation.  Throw  the  light  into  the  fixing 
eye,  and  note  the  position  of  the  reflection  of  the 
mirror  on  the  cornea,  while  the  patient  fixes  the 
mirror.  Now  direct  the  patient  to  look  at  a  small 
white  card,  which  is  held  three  or  four  feet  away 
from  him  by  an  assistant.  Throw  the  light  on  to 
the  cornea  of  the  deviating  eye,  and  manoeuvre 
the  card  till  the  reflection  of  the  image  on  the 
cornea  is  in  a  position  corresponding  to  that 
which  it  formerly  occupied  in  the  fixing  eye.  Now 
proceed  with  the  retinoscopy. 


CHAPTER   VII. 
THE  TREATMENT  OF  CONVERGENT  SQUINT. 

I  propose  to  describe  first  the  treatment  I 
adopt  in  cases  of  constant  unilateral  squint. 
Any  modification  of  treatment  required  in  occa- 
sional or  alternating  cases  will  be  considered 
afterwards. 

The  objects  to  be  kept  constantly  in  view  in 
the  treatment  of  squint  are — (a)  To  prevent 
deterioration  of  the  vision  of  the  deviating  eye, 
and  to  restore,  as  far  as  possible,  the  sight  of  this 
eye  in  cases  in  which  amblyopia  from  disuse  has 
already  been  allowed  to  occur.  (6)  To  endeavour 
to  remove  the  fundamental  cause  of  the  squint, 
by  training  the  fusion  sense  at  the  earliest  pos- 
sible age.  (c)  To  restore  the  visual  axes  to  their 
normal  relative  directions. 

There  are  five  therapeutic  measures  at  our 
disposal,  any  or  all  of  which  it  may  be  necessary 
to  use  in  our  endeavour  to  attain  these  objects, 
(i)  Optical  correction  of  any  refractive  error 
which  may  be  present.  (2)  Occlusion  of  the 
fixing  eye.  (3)  Instillation  of  atropine  into  the 
fixing  eye  only.  (4)  Training  the  fusion  sense. 
(5)  Operation. 


98  THE    TREATMENT    OF 

( i )  Optical  Correction.  —As  has  been  demon- 
strated in  chapter  iv.,  the  essential  factor  which 
allows  a  deviation  to  occur  is  a  defect  of  the 
fusion  faculty.  The  eyes  then,  being  uncon- 
trolled by  the  necessity  for  fusion,  are  for  a  time 
kept  approximately  "  straight "  by  their  motor 
coordinations.  But  they  are  in  a  state  of  unstable 
equilibrium,  and  are  ready  to  squint,  either  in- 
wards or  outwards,  in  response  to  influences  which 
would  have  no  effect  if  the  fusion  faculty  were 
normal.  In  a  very  large  proportion  of  the  cases 
it  is  the  state  of  the  refraction  which  chiefly 
determines  whether  the  eyes  shall  deviate  in- 
wards or  outwards.  Thus,  in  the  great  majority 
of  cases,  the  eyes  of  hypermetropic  squinters 
deviate  inwards,  and  the  eyes  of  myopic  squinters 
deviate  outwards.  It  is  rational  treatment,  there- 
fore, to  attempt  to  overcome  the  deviation  by 
optical  correction  of  any  refractive  error  which 
may  be  present. 

In  cases  of  simple  hypermetropia,  or  hyper- 
metropic astigmatism,  or  compound  hyperme- 
tropic astigmatism,  my  usual  practice  is  to  order 
spectacles  fully  correcting  any  astigmatism  which 
may  be  present,  and  correcting  all  but  o"5  d  of 
the  hypermetropia.  The  reason  for  the  slight 
under-correction  of  the  hypermetropia  is  this  : — 
When  the  effect  of  the  atropine,  used  for  the 
retinoscopy,  has  passed  off,  some  of  the  hyper- 
metropia will  in  any  case  become  "latent,"  so  that 


CONVERGENT    SQUINT  99 

fully-correcting  glasses,  which  gave  perfect  distant 
vision  under  atropine,  will,  when  its  effect  has 
passed  off,  make  all  distant  objects  appear  misty. 
This  blurring  of  distant  objects  not  only  shortens 
the  child's  range  of  vision  at  a  time  when  the 
acuity  of  the  physical  senses  has  the  most  marked 
effect  upon  his  mental  development,  but  the 
effort  to  see  distinctly  actually  appears  to  affect 
unfavourably  the  angle  of  the  deviation.1 

In  a  case  of  mixed  astigmatism,  the  refractive 
error  should  be  exactly  corrected. 

A  certain  percentage  of  cases  of  convergent 
squint  are  myopic.  Any  myopic  astigmatism 
should  of  course  be  exactly  corrected.  But  as 
regards  simple  myopia,  it  might  naturally  be 
thought  that  a  considerable  under-correction 
would  tend  to  lessen  the  abnormal  convergence 
by  preventing  any  effort  of  accommodation  even 
in  near  vision.  I  began  by  acting  upon  this 
assumption,  but  was  gradually  forced  by  experi- 
ence to  abandon  it.  I  find  that  the  best  results 
are  obtained  by  exactly  correcting  any  myopia 
and  myopic  astigmatism  which  may  be  present. 
Myopes  who  begin  early  to  wear  fully-correcting- 

1  I  have  taken  over  a  considerable  number  of  hospital 
squint  cases  which  were  formerly  under  the  care  of  a 
colleague,  who  used  habitually  to  over-correct  the  hyper- 
metropia  to  the  extent  of  1  D.  In  the  majority  of  these 
cases  the  deviation  became  less  within  a  few  weeks  of 
ordering  glasses  with  which  the  patients  could  see  dis- 
tinctly. 


lOO  THE    TREATMENT    OF 

glasses,  use  them  quite  comfortably  for  all  purposes, 
and  appear  to  have  as  good  a  range  of  accommo- 
dation as  emmetropes. 

In  a  case  of  anisometropia,  the  refractive  error 
of  each  eye  should  be  corrected  according  to  the 
preceding  rules.  This  applies  even  to  cases  in 
which  one  eye  is  hypermetropic  and  the  other 
myopic. 

When  glasses  are  ordered,  it  is  a  good  plan, 
especially  with  young  children,  to  continue  the 
atropine,  which  has  been  used  for  the  retinoscopy, 
until  the  glasses  arrive  from  the  optician.  It 
should  then  be  discontinued.  Even  an  infant 
soon  discovers  that  he  sees  better  with  the  glasses 
than  without  them,  and  by  the  time  the  effect  of 
the  atropine  has  passed  off,  the  wearing  of  glasses 
has  become  as  much  a  habit  as  the  wearing-  of 
clothes. 

The  glasses  should  be  worn  constantly,  except 
when  the  child  is  in  bed  at  night.  They  should 
never  be  removed  at  any  other  time,  except  for 
toilet  purposes. 

In  the  case  of  children  who  are  old  enough  to 
attend  school,  some  surgeons  order  one  pair  of 
glasses  for  distant  vision  and  a  stronger  pair  for 
reading.  I  have  tried  this  plan  and  found  it  most 
unsatisfactory.  In  changing  from  one  pair  to 
the  other  there  is  often  a  considerable  interval  in 
which  no  glasses  are  worn  at  all.  Besides,  the 
exercise  of  a  noi'mal  amount  of  accommodation  in 


CONVERGENT    SQUINT  IOI 

association  with  dynamic  convergence,  in  near 
vision,  is  a  physiological  act,  and  its  suspension 
has  not  appeared  to  me  to  have  permanently 
lessened  the  angle  of  the  squint. 

The  quality  and  fit  of  the  spectacle-frames  are 
very  important.  Steel  is  the  best  material  for 
children.  Steel  frames  of  good  quality  will 
remain  without  rust  for  a  long  time,  if  the  child 
be  kept  moderately  clean.  After  a  time,  the 
growth  of  the  child's  face  will  necessitate  larger 
frames.  For  infants  and  young  children  the 
lenses  should  be  circular,1  or  oval  with  their  long- 
axes  vertical,  in  order  that  there  shall  be  no 
temptation  for  the  child  to  look  over  them.  The 
lenses  should  be  as  large  as  possible,  and  should 
be  centred  for  distant  vision.  They  should  be  as 
close  to  the  eyes  as  they  can  be  without  touching 
the  lashes.  The  bridge  piece,  which  arches  over 
the  bridge  of  the  nose,  should  be  of  tempered 
steel,  broad,  flat,  and  strong,  and  should  be  very 
accurately  fitted.  A  broad  thin  plate  of  tortoise- 
shell,  carefully  fitted  under  the  arch  of  the  bridge 
piece,  prevents  rust  and  distributes  the  pressure 
over  a  larger  area.       Spectacles  for  children  of 

1  Circular  lenses,  however,  have  this  disadvantage — 
unless  the  spectacles  are  carefully  made,  the  lenses  are  apt 
to  rotate  in  the  frames,  so  that  the  axes  of  cylinders  become 
displaced.  This  may  be  prevented  by  putting  a  little 
Canada  balsam  in  the  groove  of  the  rim.  If  it  should  be 
necessary,  at  any  time,  to  replace  a  cracked  lens,  the 
balsam  may  be  melted  by  a  moderate  heat. 
8 


102 


THE    TREATMENT    OE 


3  years  and   upwards   should    have  flexible   curl 
sides  to  hook  behind  the  ears. 

Infants  and  very  young  children  should  have 
their  o-lasses  tied  on.  The  sides,  in  this  case, 
should  be  straight  and  should  have  a  loop  at  the 
end.  They  should  be  very  short,  only  reaching 
to  just  above  the  ear.    About  f  inch  near  the  loop 


should  be  wrapped  with  wool.  The  glasses  are 
tied  on  by  tapes,  passed  through  the  loops,  behind 
the  child's  head.  These  frames  are  very  com- 
fortable. If  the  sides  were  of  the  usual  length 
the  tapes  would  act  at  the  end  of  a  long  lever, 
causing  pressure  above  the  ear,  and  perhaps 
ulceration  of  the  tender  skin  of  the  infant. 
When  the  infant  is  put  down  to  sleep  in  the 
daytime    these   frames   are  not   removed.      These 


CONVERGENT    SQUINT  103 

very  short  sided  do  not  press  on  the  pillow  and  lift 
the  glasses  from  the  child's  face. 

It  is  usually  stated  that  children  under  three  or 
four  years  of  age  are  too  young  for  glasses.  No 
infant  is  too  young  to  wear  glasses  should  they 
be  required.  Many  of  my  squinting  patients  have 
begun  to  wear  spectacles  such  as  I  have  described, 
long  before  twelve  months  of  age. 

Of  course  young  children  sometimes  break  their 
glasses,  but  I  have  never  known  a  case  in  which 
the  eye  has  been  injured  thereby.  The  lens, 
being  held  in  the  frame,  does  not  break  into 
splinters  but  cracks  across,  or  chips  at  the  edge. 

(2)  Occlusion  of  the  Fixing  Eye. — In  the 
case  of  a  child  who  has  squinted  constantly  with 
one  eye  for  a  considerable  proportion  of  his  life, 
and  who  has  either  received  no  treatment  at  all  or 
who  has  been  merely  given  a  pair  of  glasses,  one 
usually  finds  that  the  deviating  eye  has  become 
more  or  less  blind.  If  the  ivory-ball  test  shows 
the  visual  acuity  of  this  eye  to  be  not  less  than  fs, 
the  case  may  be  treated  at  once  in  the  manner 
described  in  paragraph  3.  Often,  however,  one 
finds  that  the  blindness  has  progressed  far  beyond 
this  point,  so  that  the  power  of  central  fixation 
may  have  been  lost  and  the  visual  acuity  reduced 
to  the  ability  to  count  fingers  close  to  the  face,  or, 
in  some  cases,  even  to  bare  perception  of  light. 

In  a  young  child,  an  attempt  should  always  be 
made  to   restore,   as   for  as  possible,  the  sight  of 


04 


THE    TREATMENT    OF 


the  deviating  eye,  by  forcing  the  child  to  try  to 
use  it.  For  this  purpose  I  order  the  fixing  eye  to 
be  continuously  occluded  for  a  time.  It  is  not  a 
good  plan  to  order  the  eye  to  be  occluded  for  part 
of  each  day  only;  apart  from  the  fact  that  this  is 
not  nearly  so  rapid  and  effective  as  continuous 
occlusion,  the  child  usually  cries  every  time  the 
shade  is  applied,  so  that  the  treatment  is  seldom 
properly  carried  out.  When  the  better  eye  is 
continuously  covered,  the  child  soon  becomes 
accustomed  to  the  shade,  so  that,  after  a  day  or 
two,  he  usually  ceases  to  object  to  it. 

There  are  several  methods  of  occluding  an  eye. 
each  of  which  may  be  useful  in  certain  cases. 
For  infants,  a  gauze  pad  secured  by  a  few  turns  of 
bandage  answers  well.  In  the  case  of  children 
who  are  beginning  to  get  about,  the  gauze  pad 
should  be  held  in  place  by  strips  of  strapping- 
plaster.  Children  who  are  well  cared  for  may 
have  the  pad  changed  every  morning.  Hospital 
patients,  however,  often  leave  the  pad  undis- 
turbed for  three  or  four  weeks  without  any  harm 
resulting. 

If  the  child  has  a  reliable  nurse  in  constant 
attendance  it  may  be  sufficient  to  pack  cotton 
wool  behind  the  spectacle  lens.  The  cotton  wool 
pad  must  be  carefully  applied  and  the  child  will 
require  constant  supervision,  or  he  will  push  the 
pad  upwards  and  outwards  and  peep  down  the 
side  of  his  nose.     The  gauze  pad  and  strapping  is 


CONVERGENT    SQUINT  1C>5 

the  only  possible  method  for  hospital  patients, 
whose  parents  are  seldom  able  to  give  them  much 
attention. 

I  examine  the  child  again  at  the  end  of  two  or 
three  weeks.  If  the  vision  of  the  deviating  eye 
be  improved  sufficiently,  the  shade  is  discontinued 
and  the  case  treated  as  described  in  paragraph  3. 
If  not,  the  fixing  eye  is  occluded  for  another 
month,  after  which  the  child  is  again  examined. 
If  occlusion  of  the  fixing  eye  is  going  to  do  much 
good,  one  usually  finds  a  very  great  improvement 
in  the  vision  of  the  squinting  eye  within  a  fort- 
night. If  this  improvement  has  not  taken  place 
at  the  end  of  two  months  it  is  seldom  worth  while 
to  continue  the  shade. 

(3)  Instillation  of  Atropine  into  the  Fixing 
Eye  Only. — Atropine  has  the  property  of  tem- 
porarily paralysing  the  ciliary  muscle,  and  so 
suspending  the  power  of  accommodation  of  the 
eye.  When,  therefore,  atropine  is  instilled  into  a 
normal  emmetropic  eye,  or  an  eye  whose  refrac- 
tive error  is  corrected  by  glasses,  this  eye  still 
sees  distant  objects  clearly,  but  is  unable  to  focus 
near  objects.  An  unatropised  eye  whose  vision 
is  only  one-sixth  or  even  one-tenth  of  the  normal, 
is  able  to  see  objects,  at  the  reading  distance, 
more  clearly  than  a  normal  eye  whose  accom- 
modation is  paralysed  by  atropine. 

In  the  case  of  a  young  patient,  the  visuai 
acuity  of  whose  squinting  eye  has  been  shown  by 


106  THE    TREATMENT    OF 

the  ivory-ball  test  to  be  not  much  less  than  g%,  I 
order  atropine  to  be  put  into  the  fixing  eye  only 
every  morning.  The  child,  of  course,  wears  his 
glasses  at  the  same  time.  He  will  be  unable  to 
see  distinctly  his  toys  and  picture-books  with  the 
atropised  fixing  eye.  But  he  quickly  discovers 
that,  by  making  a  conjugate  lateral  movement  of 
both  eyes  until  he  has  brought  the  squinting  eye 
to  bear  on  these  near  objects,  he  can  see  them 
much  more  clearly.  He  acquires  the  habit  of 
always  using  the  (atropised)  better  eye  for  dis- 
tant vision  and  his  (unatropised)  worse  eye  for 
near  vision.  In  this  way  the  worse  eye  is  most 
efficiently  exercised,  and  amblyopia  ex  anopsia 
prevented.  And,  in  a  case  in  which  a  consider- 
able degree  of  blindness  has  already  been  acquired, 
one  finds  at  each  visit,  if  the  child  be  young 
enough,  a  steady  improvement  in  vision.  In 
many  cases,  after  a  few  weeks  or  months  of  this 
treatment,  the  vision  of  this  previously  amblyopic 
eye  becomes  perfect,  or  nearly  so.  When  the 
visual  acuity  of  the  (unatropised)  "deviating 
eye  "  approaches  the  normal  the  child  uses  this 
eye  always  both  in  near  and  distant  vision,  and 
turns  in  the  (atropised)  "fixing  eye"  instead. 
I  then  stop  the  atropine  for  two  or  three  weeks  to 
see  what  will  happen.  Usually  the  child  returns 
to  his  old  habit  of  squinting  with  the  eye  with 
which  he  squinted  at  first,  and  fixing  with  the 
"  fixing  eye."      In  this  case  1  order  atropine  every 


CONVERGENT    SQUINT  \Oj 

morning  for  the  fixing  eye  only  for  the  first  seven 
days  in  each  month.  It  occasionally  happens,  in 
the  case  of  a  young  child,  that,  on  discontinuing 
the  atropine,  what  was  originally  the  fixing  eye 
continues  to  exhibit  the  deviation.  The  case 
may  be  left  for  three  or  four  weeks,  but  care 
must  be  taken  lest  this  originally  fixing  eye 
now  become  amblyopic  (see  Case  B,  83,  and 
Case  D,  332,  chapter  v.).  The  balance  may 
easily  be  kept  by,  if  necessary,  atropising  the 
other  eye  for  a  few  days. 

The  use  of  atropine  for  the  fixing  eye  only  is 
an  exceedingly  efficient  curative  measure.  A 
young  child  spends  at  least  half  his  waking  hours 
in  looking  at  near  objects.  So  that  when  he 
uses  the  (atropised)  "  fixing  eye  "  in  distant  vision 
and  the  (unatropised)  "squinting  eye"  in  near 
vision,  this  is  equivalent  to  perfect  occlusion  ot 
the  "  fixing  eye  "  for  at  least  half  of  each  day. 
And  when  his  glasses  are  taken  off  for  any 
purpose,  if  he  has  much  refractive  error,  he  turns 
in  the  atropised  "  fixing  eye "  and  uses  the 
unatropised  worse  eye,  even  in  distant  vision. 

As  regards  the  form  in  which  the  atropine  is 
used,  I  usually  order  one  drop  of  a  1  per  cent, 
solution  of  atropine  sulphate  to  be  put  into  the 
fixing  eye  only,  every  morning.  It  may  be 
inserted  with  a  "dropper"  or,  better  still,  with 
a  small  camel  hair  brush  or  feather.  Atropine 
ointment  answers  the  same  purpose.     The  lower 


108  THE    TREATMENT    OF 

lid  should  be  drawn  down,  and  a  small  piece 
inserted  into  the  conjunctival  sac  with  a  glass 
rod.  Lamellae  containing  ^oo  to  T^  of  a  grain 
of  atropine  sulphate  may  be  used  instead,  but 
nurses  usually  find  them  rather  difficult  to  insert. 

I  always  see  the  child  again  within  a  month  of 
beginning  this  treatment,  and  after  that  at  intervals 
of  one  or  two  months,  according  to  the  nature  of 
the  case.  In  order  that  there  may  be  no  mistake, 
the  mother  is  given  a  card  on  which  are  written 
the  directions  and  the  date  of  the  next  visit.  The 
treatment  is  continued  until  the  visual  acuity  of 
the  squinting  eye  becomes  equal  to  that  of  the 
fixing  eye,  or  until  no  further  improvement  can  be 
got.  Having  employed  this  method  for  main- 
years,  and  in  a  very  large  number  of  cases,  I  am 
able  to  state  positively  that  there  is  no  danger  of 
its  causing  any  permanent  impairment  of  the 
power  of  accommodation. 

This  treatment  will  always  prevent  the  deviating 
eye  from  #becoming  amblyopic.  Its  efficiency  in 
curing  amblyopia  which  has  already  been  acquired 
will  be  greater  the  younger  the  child  and  the 
more  recent  the  deviation.  After  about  seven 
years  of  age  usually  not  much  improvement  in 
vision  can  be  obtained,  though  I  have  met  with 
many  exceptions  to  this  rule. 

Of  course,  carefully  keeping  the  fixing  eye  tied 
up  for  not  less  than  half  of  the  child's  waking- 
hours  would  answer  as  well,  if  it  could  be  really 


CONVERGENT    SQUINT  IO9 

clone.  But,  whatever  the  mother  and  nurse  may 
promise  at  first,  they  will,  after  a  few  weeks,  find 
the  amount  of  supervision  required  too  great  a 
tax  on  their  time  and  patience.  But  even  the 
hard-worked  mother  of  a  large  family,  attending 
a  hospital  out-patient  clinic,  finds  it  no  trouble  to 
put  a  drop  of  atropine  into  the  fixing"  eye  only 
every  morning,  for  as  long  as  it  may  be  required. 

A  disastrous  practice,  adopted  by  many  surgeons 
and  invariably  recommended  in  books,  is  that  of 
ordering  atropine  for  both  eyes  for  children  who  are 
supposed  to  be  too  young  for  glasses.  The  object, 
of  course,  is  to  lessen  the  convergence  by  para- 
lysing the  accommodation.  Atropine,  used  in  this 
way,  never  brings  about  a  permanent  cure  of  the 
squint,  though  it  occasionally  causes  a  temporary 
suspension  of  the  deviation.  But  the  deviating 
eye  is  usually  the  more  ametropic,  so  that  to 
paralyse  its  accommodation  with  atropine  is  the 
very  way  to  ensure  that  this  eye  shall  never  under 
any  circumstances  be  used.  The  most  hopeless 
cases  one  sees,  of  blindness  of  the  squinting  eye, 
are  those  which  have  been  treated  with  atropine 
for  both  eyes  for  a  few  months. 

(4)  Training  the  Fusion  Sense. — In  a  case 
of  unilateral  or  accidentally  alternating  squint, 
if  the  child  is  brought  early  enough,  I  endeavour 
to  remove  the  fundamental  cause  of  the  squint  by 
training  the  fusion  sense.  For  this  purpose  I  use 
an    instrument    which     I     have    called    "  amblvo- 


1  IO  THE    TREATMENT    OF 

scope."  A  description  of  the  amblyoscope  and 
of  the  method  of  training"  the  fusion  faculty  will 
be  found  in  the  next  chapter.  The  favourable 
time  for  fusion  training  is  between  the  ages  of 
three  and  five  years.  In  children  under  three 
years  of  age  this  treatment  is  apt  to  be  rather 
difficult,  though  I  have  succeeded  in  many  cases. 
After  five  years  of  age  the  fusion  training  takes 
longer,  and  a  much  less  powerful  "desire  for 
binocular  vision"  is  obtained.  After  six  years  of 
age  it  is  seldom  worth  while  to  attempt  fusion 
training  at  all.  It  is  true  that,  occasionally,  a 
patient  who  has  squinted  for  many  years  may 
have  a  sort  of  binocular  vision  when  his  deviation 
is  corrected  by  operation  at  a  much  later  date. 
But  this  small  degree  of  fusion  sense  is  not  a 
fresh  acquisition.  He  had  it  before  he  squinted, 
but  it  was  too  feeble  to  prevent  the  occurrence 
of  a  deviation,  or  even  to  cause  diplopia. 

Normally  the  iusion  faculty  begins  to  develop 
at  a  very  early  age,  and,  I  think,  reaches  its  full 
development  by  about  the  end  of  the  sixth  year. 
The  education  of  the  fusion  faculty,  at  a  time 
when  this  should  normally  be  developing,  is  very 
rapid,  easy,  and  charming  in  its  results.  "  Stereo- 
scopic exercises,"  undertaken  at  a  time  when  the 
child  is  old  enough  to  take  an  intelligent  interest 
in  the  process,  are  infinitely  tedious  and  dis- 
appointing. 

Of  course,  one  should    never  omit   fusion  train- 


CONVERGENT    SQUINT  I  I  1 

ing  in  any  suitable  case  which  presents  itself  in 
private  practice.  But  in  a  large  hospital  clinic,  it 
is  physically  impossible  to  find  time  for  it  except 
in  a  few  selected  cases. 

(5)  Operation.  —  In  cases  of  convergent  squint 
in  which  the  deviation  is  not  overcome  by  other 
means,  operation  becomes  necessary.  Two  op- 
erative procedures  are  employed  either  separately 
or  in  combination.  They  are  tenotomy  of  the 
internal  rectus  muscle  and  advancement  of  the 
external  rectus  muscle. 

Tenotomy  of  the  internal  rectus  consists  in  a 
division  of  the  tendon  of  this  muscle  at  its  inser- 
tion into  the  globe.  The  eye  then  rotates  out- 
wards to  an  uncertain  degree.  This  outward 
rotation  usually  tends  to  increase  as  time  goes  on. 
The  eye  also  falls  forward  to  a  slight  extent,  so 
that  the  tenotomised  eye  is  more  prominent  than 
its  fellow  and  its  palpebral  fissure  wider.  A  per- 
manent weakness  of  inward  rotation  (adversion) 
of  this  eye  is  also  produced. 

In  order  to  advance  a  muscle,  the  tendon  is 
separated  from  the  globe  at  its  insertion.  It  is 
usually  then  shortened  by  removal  of  more  or  less 
of  the  tendon  and  muscle.  The  cut  end  of  the 
muscle  is  then  secured  to  the  globe  at  a  point 
further  forward,  nearer  the  cornea  than  its  original 
insertion.  By  a  properly  performed  advancement 
the  eye  is  rotated  to  exactly  the  extent  required. 
The  results  obtained  by  the  advancement  opera- 


112  THE    TREATMENT    OF 

tion  described  in  chapter  xii.  are  permanent, 
tending-  neither  to  increase  nor  to  decrease  with 
time.  Both  the  power  and  extent  of  the  rotation 
of  the  eye  in  the  direction  of  action  of  the 
advanced  muscle  are  increased.  The  rotation  of 
the  eye  in  the  opposite  direction  is  not  in  any 
case  weakened  in  force,  though  in  extreme  cases 
its  extent  may  be  slightly  diminished.  If  the 
abnormal  convergence  does  not  exceed  200  or  25°, 
its  cure  by  advancement  of  the  external  rectus 
muscle  rarely  causes  any  noticeable  degree  of 
retraction  of  the  globe.  If  the  deviation  be  of 
higher  degree  than  this,  I  usually  combine  the  ad- 
vancement of  the  external  rectus  with  tenotomy  of 
the  internal  rectus,  in  order  to  avoid  any  retraction. 

The  operations  on  the  external  ocular  muscles 
are  fully  described  and  discussed  in  chapter  xii. 

The  question  may  naturally  be  asked  :  "As  the 
deviation  in  a  case  of  convergent  squint  is  not 
due  to  a  defect  of  the  muscles,  why  should  one 
ever  seek  to  remedy  this  deviation  by  shortening 
a  muscle  ?"  The  answer  is  this — In  the  presence 
of  a  defect  of  the  fusion  faculty,  refractive  error 
may  cause  a  deviation,  or  the  equilibrium  of  the 
convergence  centre  may,  in  some  unknown  way, 
be  upset  by  a  fright,  blow  on  the  head,  whooping- 
cough,  &c.  If  one  is  able  to  train  the  fusion 
sense  early,  the  desire  for  binocular  vision  is, 
more  often  than  not,  in  itself  sufficient  to  over- 
come the  deviation  and  produce  a  perfect  cure,  in 


CONVERGENT    SQUINT  I  I  3 

spite  of  any  adverse  influences.  In  many  cases, 
optical  correction  of  refractive  error  causes  the 
deviation  to  disappear.  In  other  cases,  as  one 
cannot  act  directly  upon  the  nervous  centre  which 
reerulates  convergence,  one  has  to  be  content  to 
act  upon  the  peripheral  motor  organs.  Take  an 
illustration — One  is  driving  a  pair  of  horses. 
Suppose  the  off-side  horse  has  a  habit  of  boring 
to  the  left.  If  any  cause  can  be  found  (such  as 
sore  shoulder),  one  may  cure  the  habit  by  remov- 
ing this  cause.  If  not,  it  is  a  reasonable  proceed- 
ing to  overcome  his  "  deviation  "  to  the  left  by 
shortening  the  off-side  branch  of  the  right  rein. 

The  angle  of  the  deviation  is  measured  at 
each  visit.  If  the  measurements  show  a  steady 
decrease,  of  course,  no  operation  is  indicated 
under  any  circumstances.  In  the  case  of  a  young 
child  whose  fusion  sense  I  have  succeeded  in 
developing  by  means  of  the  amblyoscope,  if  the 
deviation  does  not  decrease  at  a  reasonable  rate 
I  have  recourse  to  operation.  If  the  angle  of  the 
squint  is  not  higher  than  200  or  250,  I  advance 
the  rectus  externus  muscle  without  tenotomising 
the  internus.  If  the  degree  is  higher  than  this,  I 
tenotomise  the  internus  at  the  same  time,  not 
because  all  the  rotation  required  cannot  be  pro- 
duced by  advancement  alone,  but  in  order  to 
avoid  retraction  of  the  globe.  This  child's  eyes 
having  been  put  approximately  straight,  his 
trained  fusion  sense  finds  its  expression  in  the  act 


114  THE    TREATMENT    OF 

of  binocular  vision,  and  a  perfect  and  permanent 
cure  results. 

In  a  case  in  which  I  expect  to  get  binocular 
vision,  I  never  perform  tenotomy  of  the  rectus 
internus  except  in  combination  with  advancement 
of  the  externus.  I  once  used  to  do  so  in  hospital 
practice,  occasionally,  for  want  of  beds.  Some 
of  these  patients  have  since  suffered  from  insuf- 
ficiency of  convergence,  and  pain  in  the  eyes  in 
near  vision.  In  two  or  three  cases,  in  which 
tenotomy  was  followed  by  divergence,  I  have  had 
to  advance  the  tenotomised  muscles.  It  very 
rarely  happens  that  any  evil  consequences  follow 
tenotomy  of  the  internal  rectus  when  combined 
with  advancement  of  the  external  rectus  in  high 
degrees  of  squint.  Perhaps  this  is  because  only  a 
small  part  of  the  total  rotation  is  produced  by 
the  tenotomy,  the  advancement  of  the  opponent 
muscle  immediately  tightening  up  everything  and 
correcting  any  tendency  to  proptosis. 

If  there  is  no  hope  of  getting  binocular  vision, 
so  that  cure  of  the  deformity  is  all  that  can  be 
accomplished,  I  prefer  not  to  operate  until  I  am 
able  to  do  so  under  cocaine.  The  eyes  are  then 
put  exactly  "straight"  by  advancement  of  the 
external  rectus  muscle  of  the  deviating  eye,  with 
or  without  tenotomy  of  the  internal  rectus  of  this 
eye.  One  not  infrequently  sees  a  patient  whose 
rectus  internus  has  at  some  previous  time  been 
tenotomised,  producing  proptosis  of  the  eye,  but 


CONVERGENT    SQUINT  115 

still  leaving  some  degree  of  convergent  squint. 
In  this  case  an  accurately  performed  advance- 
ment of  the  external  rectus  will  cure  the  devia- 
tion, and  at  the  same  time  draw  the  eye  back 
into  its  proper  position  in  the  orbit. 

Simple  tenotomy  is  an  unsatisfactory  opera- 
tion, even  in  cases  in  which  binocular  vision  is 
out  of  the  question.  The  tendon  is  divided,  and 
the  result  cannot  in  any  individual  case  be  fore- 
told. Some  cases  turn  out  well,  others  do  not. 
The  effect  produced  by  a  tenotomy  is,  on  an 
average,  about  130,  though  it  varies  very  widely  in 
different  cases.  The  effect,  as  a  rule,  increases  for 
the  first  three  or  four  months  after  the  operation, 
after  which  it  usually  remains  about  stationary. 
But  in  some  cases,  however  skilfully  the  tenotomy 
may  have  been  performed,  its  effect  continues  to 
increase  for  years,  until  a  divergent  squint  is 
produced — a  more  hideous  deformity  than  that 
which  the  operation  was  intended  to  cure. 

There  is  one  condition  in  which  simple  tenotomy 
is  sometimes  advisable.  One  occasionally  sees  a 
patient  whose  eyes  in  distant  vision  are  normally 
directed,  but  who  turns  in  one  or  other  eye  to  an 
extreme  degree  in  looking  at  a  near  object,  even 
in  the  absence  of  uncorrected  refractive  error. 
One  has  no  means  of  diminishing  the  excessive 
activity  of  his  nervous  centre  for  dynamic  con- 
vergence, but  the  case  may  be  treated  empirically 
by  tenotomy  of  an  internal  rectus. 


I  I  6  THE    TREATMENT    OF 

The  internal  rectus  should  never  be  tenot- 
omised  in  any  case  in  which  dynamic  conver- 
gence is  subnormal. 

A  patient  requires  very  little  care  after  the 
operation  of  tenotomy.  This  is  a  great  advan- 
tage in  a  crowded  hospital  clinic.  But  I  think 
tenotomy  owes  its  popularity  chiefly  to  the 
extreme  facility  of  its  execution,  almost  no  special 
knowledge  being  required.  An  accurately  per- 
formed advancement,  on  the  other  hand,  is  one 
of  the  most  delicate  (and  satisfactory)  operations 
in  surgery. 

Alternating  convergent  squint. — The  treatment 
of  an  accidentally  alternating  squint  is  similar  to 
that  of  a  unilateral  squint,  except  that  there  is 
no  acquired  amblyopia  to  be  remedied.  It  must 
not  be  forgotten,  however,  that  such  a  case,  if 
neglected,  may  become  unilateral,  and  that  the 
deviating  eye  may  then  become  amblyopic. 

Essentially  alternating  squints  are,  fortunately, 
not  very  common.  The  treatment  consists  in 
optical  correction  of  any  ametropia  which  may  be 
present,  followed,  in  the  majority  of  cases,  by 
operation.  Fusion  training  is  impossible,  as  there 
is  a  total  congenital  absence  of  the  faculty  of 
acquiring  fusion.  For  this  reason,  if  operation  be 
required,  I  postpone  it  until  the  patient  is  old 
enough  to  permit  its  performance  under  a  local 
anaesthetic. 

Occasional  convergent  squint. — The  majority  of 


CONVERGENT    SQUINT  I  I  7 

occasional  squints  in  young  children  are  of  the 
premonitory  variety.  Optical  correction  of  any 
refractive  error  which  may  be  present  usually 
prevents  the  recurrence  of  the  deviation,  and  so 
allows  the  natural  development  of  the  fusion  sense 
to  proceed. 

Quite  half  the  cases  which  are  commonly 
supposed  to  be  occasional  squints,  occurring  in 
older  children  and  adults,  are  really  examples  of 
esophoria  (see  chapter  xi.). 

If  one  whose  fusion  faculty  is  perfect  suffers 
from  anisometropia  of  so  high  a  degree  as  to 
render  the  act  of  binocular  vision  difficult,  he  will 
be  likely  to  manifest  an  occasional  squint.  Glasses 
should  be  ordered  which  give  the  sharpest  vision 
in  each  eye,  even  though  one  eye  be  hyper- 
metropic and  the  other  myopic.  The  patient  will 
soon  become  accustomed  to  the  inequality  in  the 
size  of  the  two  images.  An  occasional  squint 
may  be  caused  by  hypermetropia  in  a  patient 
whose  fusion  sense  is  feeble. 

Vertical  deviation. — If  operation  be  required 
in  a  case  of  true  vertical  deviation,  this  should 
consist  in  advancement  of  the  inferior  rectus 
muscle,  or  complete  central  tenotomy  of  the  su- 
perior rectus,  of  the  eye  which  turns  up.  The 
inferior  rectus  should  never  be  tenotomised. 

Apparent  vertical  deviation  (p.  37)  requires  no 
treatment  beyond  that  of  the  constant  squint. 


n8 


CHAPTER    VIII. 

THE  METHOD  OE  TRAIN I XG  THE    FUSION 

SEXSE. 

For  more  than  half  a  century  attempts  have, 
from  time  to  time,  been  made  to  teach  squinting 
patients  to  use  both  eyes  together,  by  means  of 
exercises  with  some  form  of  stereoscope.  Among 
the  stereoscopes  used  for  this  purpose  are  Wheat- 
stone's  original  instrument,  Brewster's  and  Helm- 
holtz's  stereoscopes,  Hering'shaploscope,  Holme's 
stereoscope,  and,  more  recently,  Javal's  "  Stereo- 
scope a  cinq  mouvements,"  Priestley  Smith's 
"  Heteroscope,"  Landolt's  and  Parinaud's  stereo- 
scopes, and  very  many  other  more  or  less  similar 
instruments.  Most  of  these  are  so  arranged  that 
they  can  be  adapted  to  suit  the  angle  of  the 
patient's  squint.  But  the  proportion  of  cases  in 
which  they  can  be  used  is  very  small,  owing  to 
the  suppression  of  the  vision  of  the  patient's 
deviating  eye.  J  aval  attempted  to  overcome  this 
suppression  by  prolonged  occlusion  of  one  or 
other  eye,  in  the  hope  that,  when  at  last  both  eyes 
were  uncovered,  the  patient  might  have  diplopia. 
All  these  instruments  are  intended  for  the  use  of 
patients  who  are  old  enough  to  intelligently  follow 
the  directions  given  them. 


FUSION    TRAINING  119 

Probably  most  ophthalmic  surgeons  have,  at 
some  time  or  other,  been  in  the  habit  of  ordering 
"  stereoscopic  exercises  "  in  cases  of  convergent 
squint,  and  have,  after  careful  trial,  given  them 
up  as  useless.  The  reason  of  their  failure  is  the 
very  early  age  at  which  the  fusion  sense  normally 
develops.  Fusion  training,  to  be  of  any  material 
benefit,  must  be  undertaken  within  this  normal 
period  of  development. 

Fusion  training  of  young  squinters  under  five 
years  of  age  is  in  suitable  cases,  quickly  and 
easily  accomplished,  and  the  results  obtained  are 
most  striking  and  gratifying.  Between  five  and 
six  the  treatment  is  apt  to  take  longer,  and  the 
results  to  be  less  perfect.  After  the  age  of  six 
or,  at  the  latest,  seven  years,  the  results  are,  from 
the  patient's  point  of  view,  not  worth  the  time 
and  trouble  which  they  cost. 

There  are  two  great  difficulties  in  the  way  of 
fusion  training  in  the  case  of  young  children  :  — 

(i)  Though  the  visual  acuity  of  the  child's 
deviating  eye  may  perhaps  be  perfect,  the  vision 
of  this  eye  is  suppressed,  so  that  he  is  ordinarily 
unable  to  receive  impressions  from  it  except  when 
the  other  eye  is  closed. 

(2)  The  child  is  far  too  young  to  understand 
the  purpose  of  fusion  training  or  to  follow  the 
directions  of  the  surgeon.  He  will,  therefore, 
only  permit  the  exercises  so  long  as  he  finds 
them  attractive  and  interesting. 


120  FUSION    TRAINING 

After  many  experiments,  I  devised  an  in- 
strument with  the  help  of  which  I  have  to 
a  great  extent  succeeded  in  overcoming  these 
difficulties.  I  have  called  it  "amblyoscope" — 
an  instrument  by  means  of  which  a  non-seeing 
eye  is  trained  to  take  its  share  in  vision.  The 
amblyoscope  has  retained  its  present  form  since 

1895. 

The  Amblyoscope^ — The  instrument  consists  of 
two  halves  joined  together  by  a  hinge.  Each  half 
consists  of  a  very  short  brass  tube  joined  to  a 
longer  tube  at  an  angle  of  1200.  At  the  angle  of 
junction  of  the  tubes  is  an  oval  mirror,2  protected 
on  the  outside  by  an  oval  plate  of  brass.  Each 
half  of  the  instrument  has  at  its  distal  end  an 
object-slide  carrier,  and  at  its  proximal  end  a 
convex  lens  having  a  focal  length  of  five  inches 
— the  distance  of  the  reflected  image  of  the  object- 
slide.  In  front  of  each  lens  is  a  slot  into  which 
a  prism,  axis  vertical,  may  be  inserted  if  required. 
The  diameter  of  the  tubes  is  \\  inch. 

1  The  amblyoscope  is  made  by  Mr.  Hawes,  optician, 
79,  Leadenhall  Street,  London,  E.C.,  and  by  the  principal 
manufacturing  opticians  in  England  and  abroad. 

2  The  mirrors  must  be  extremely  thin.  If  they  are  merely 
pieces  of  ordinary  thick  mirror  glass  there  will  be  blurring, 
owing  to  reflection  from  the  surface  of  the  glass  as  well  as 
from  that  of  the  mercury.  Mirrors  silvered  on  the  surface 
answer  well  but  are  easily  scratched.  I  have  tried  polished 
speculum  metal.  This  is  satisfactory  but  very  expensive. 
The  mirrors  must  be  accurately  set  perpendicular  to  the 
plane  of  the  tubes. 


FUSION    TRAINING 


121 


A  brass  arc1  connects  the  two  parts  of  the 
instrument,  being  clamped  on  one  side  by  a  bind- 
ing screw  set  in  a  long  slot  and  on  the  other  by  a 
binding  screw  set  in  a  short  slot.  When  the  screw 
in  the  long  slot  is  loosened,  the  two  parts  of  the 
instrument  can  be  brought  together  to  suit  a  con- 


vergence of  the  visual  axes  up  to  6o°,  or  separated 
to  suit  a  divergence  of  as  much  as  300.  When 
this  screw  is  tightened  and  the  screw  in  the  short 
slot  loosened,  an  amplitude  of  movement  of  about 
io°  only  is  permitted. 

The  convex  lenses  of  course  render  unnecessary 
any  adjustment  of  the  instrument  for  the  patient's 
inter-pupillary  width. 

1  In  the  earlier  forms  of  the  instrument  I  had  the  arc 
marked  in  degrees,  as  I  thought  that  the  instrument  might 
also  be  used  for  the  subjective  measurement  of  hetero- 
phorias.  I  found,  however,  that  it  was  of  no  use  for  this 
purpose.  No  instrument,  in  which  the  objects  looked  at 
are  near  the  eyes,  is  reliable  for  measuring  heterophoria. 
Though  the  lenses  render  accommodation  unnecessary,  the 
patient  unconsciously  accommodates  for  an  object  which  he 
knows  is  near. 


122 


FUSION    TRAINING 


Illumination  of  the  object-slides. — Each  object- 
slide  is  illuminated  by  a  separate  electric  lamp. 

A  stout  brass  rod,  about  two  feet  in  length,  is 
held  in  brass  sockets  at  each  end.  The  brass 
sockets   are  screwed  to  a  board,  which  is  firmly 


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Fig. 


secured  to  the  wall  of  the  consulting  room  in  such 
a  position  that  the  brass  rod  is  vertical.  A  brass 
collar  slides  up  and  down  the  vertical  rod,  and  is 
fixed  by  a  thumb-screw  at  the  height  required. 
This  collar  supports  two  independent  collars,  each 
of  which  has  attached  to  it  a  long  horizontal  arm. 
Each  of  these  arms  is  four  feet  in  length,  and  is 


FUSION    TRAINING  I  23 

free  to  move  in  a  horizontal  plane  independently 
of  the  other.  An  electric  lamp  is  suspended  under 
each  horizontal  arm  from  a  ring  which  slides  along 
the  arm.  The  illumination  of  either  of  the  object 
slides  in  the  amblyoscope  may  be  separately  in- 
creased or  diminished  by  bringing  its  lamp  nearer 
or  pushing  it  further  away. 

Before  I  had  electric  light  I  used  two  paraffin 
lamps  on  a  table,  varying  the  distance  of  each 
lamp  and  the  height  of  the  flame  as  required. 
This  simple  plan  answers  just  as  well  but  is  not 
quite  so  convenient. 

The  object-slides.— -Fig.  13  shows  the  familiar 
vertical  slits  with  their  control  marks.  They  are 
not  used  for  fusion  training,  one  could  not  induce 
a  young  child  to  study  such  uninteresting  objects. 
They  are  shown  because  they  are  useful  in  making 
experiments  with  older  persons. 

The  devices  used  in  fusion  training  are  of  three 
classes  : — 

( 1 )  Those  which  do  not  require  any  blending 
of  images,  but  only  simultaneous  vision  of  dis- 
similar objects  with  the  two  eyes.  Fig.  14, 
showing  a  cage  on  one  slide  and  a  bird  on  the 
other,  is  an  example.  Other  pairs  of  devices  of 
this  class  are  a  clown  and  a  hoop,  a  mouse  and  a 
trap,  a  clock-face  and  hands,  &c. 

(2)  Devices  of  the  second  class,  of  which  figs. 
16  and  17  are  examples,  require  true  fusion  of 
images  in  order  that  the  full  picture  may  be  seen. 


I24 


FUSION    TRAINING 


Fig.  13. 


Fig.  14. 


^w 

mn 

11 

FUSION    TRAINING 


125 


Fig.  16. 


Fig.  17. 


Fig.  18. 


126  FUSION    TRAINING 

The  pictures  on  each  pair  of  slides  are  exactly 
similar,  except  that  part  of  the  design  is  omitted 
in  one  and  a  different  part  in  another.  For 
example,  in  fig  16  a  leg  is  omitted  in  one  slide 
and  the  hat  in  the  other.  A  child  who  blends 
the  images  sees  a  man  with  two  legs  and  a 
hat. 

(3)  Devices  such  as  fig.  18  can  only  be  appre- 
ciated by  patients  who  have  the  third  grade  of 
binocular  vision,  the  sense  of  perspective. 

The  designs  are  drawn  on  ij  inch  squares  of 
thin  translucent  paper.  The  paper  is  then  pasted 
on  squares  of  glass.  There  is  no  difficulty  in 
making  designs  of  the  first  class.  Object  slides  of 
the  second  class  are  made  as  follows  : — I  draw,  on 
pieces  of  paper  1^  inch  square,  rough,  simple 
pictures,  such  as  a  horse,  a  clown,  a  cow,  a  man 
with  a  hat  and  pipe,  &c,  the  more  grotesque  the 
better  the  children  seem  to  like  them.  I  then 
make  two  tracings  of  each  on  the  translucent 
paper,  omitting  a  different  part  of  the  picture  in 
each  tracing.1 

Ftision  Training. — The  education  of  the  fusion 

1  "  Stereoscopic  views"  are  of  no  practical  use  whatever 
for  fusion  training.  But  I  once  had  made  some  tiny  trans- 
parent stereoscopic  photographs  to  fit  the  amblyoscope. 
My  idea  was  that  a  child  who  wearied  of  my  own  artistic 
efforts  might  be  shown  some  of  these  views,  occasionally, 
by  way  of  a  change.  But  I  found  that  young  children  took 
no  interest  in  them.  They  much  preferred  simple  pictures 
which  they  could  understand. 


FUSION    TRAINING  I  27 

sense  should  be  undertaken  at  the  earliest  possible 
age.  I  repeat  this  because  it  is  of  supreme  import- 
ance—the only  key  to  success.  In  the  case  of  a 
child  of  average  intelligence,  it  is  quite  easy  to 
use  the  amblyoscope  at  the  age  of  three  to  three 
and  a  half  years.  I  have  succeeded  in  many  cases 
before  three  years  of  age,  but  it  is  often  rather 
difficult  to  keep  the  attention  of  these  very  young 
children. 

The  deviating  eye  must  not  be  too  blind.  In 
cases  which  have  received  efficient  treatment  since 
soon  after  the  first  appearance  of  the  deviation, 
the  vision  of  each  eye  is  nearly  always  perfect. 
But,  in  neglected  or  inefficiently  treated  cases,  the 
deviating  eye  is  often  very  blind.  (Compare 
Tables  III.  and  V.,  pp.  76  and  77).  I  do  not  as 
a  rule  attempt  fusion-training  in  a  child  who, 
after  all  possible  means  have  been  employed  to 
restore  the  sight  of  the  deviating  eye,  is  still 
unable  to  see  the  1  inch  ivory  ball  at  six  yards. 

A  squinter  sees  with  his  fixing  eye  only,  or, 
under  certain  circumstances,  with  the  deviating 
eye  only,  but  not  with  both  simultaneously.  The 
first  step  in  the  treatment  is  to  overcome  this  sup- 
pression. If  the  child  has  any  refractive  error  this 
is  corrected  by  spectacles.  It  occasionally  happens 
that  the  mirror  test  (p.  80)  has  revealed  a  slight 
vertical  deviation.  In  this  case  corresponding 
prisms,  axes  vertical,  are  inserted  in  the  slots  in 
front  of  the  lenses.      Seated  in  a  chair  facing  the 


128  FUSION    TRAINING 

lighting  apparatus,  I  take  the  child  on  my  knee 
and  adapt  the  amblyoscope'  roughly  to  the  angle 
of  his  squint.  I  put  in  the  instrument  first  a  pair 
of  object-slides  which  requires  no  fusion,  only 
simultaneous  perception — those  shown  in  fig.  15, 
for  example.  Each  light  is  at  first  about  4  feet 
away  from  its  object  slide.  Suppose  the  cage  is 
before  the  fixing  eye  and  the  bird  before  the 
squinting  eye.  The  child,  on  looking  into  the 
amblyoscope,  will  see  only  the  cage.  I  tell  him 
to  look  for  the  bird,  while  I  bring  the  light  before 
the  deviating  eye  nearer  and  nearer.  At  last  a 
point  is  reached  when  the  illumination  of  the 
object-slide  before  the  deviating  eye  becomes  so 
intense  that  the  vision  of  this  eye  can  no  longer 
be  suppressed.  The  child  suddenly  says  he  sees 
the  bird  he  was  told  to  look  for.  But  he  has  now 
usually  lost  sight  of  the  cage  before  the  fixing 
eye.  The  relative  distances  of  the  lights  are 
then  readjusted  until,  after  a  few  minutes  of 
alternation  of  the  vision  of  the  two  eyes,  the  child 
sees  the  bird  and  the  cage  simultaneously.  The 
child    is   then  allowed   to  grasp  the   amblyoscope 


1  I  used  occasionally  to  drop  the  instrument  and  break 
some  part  of  it,  until  Dr.  Ernest  Maddox  suggested  the 
simple  expedient  of  slinging  it  from  the  ceiling  by  means  of 
a  string  and  pulley  and  little  leaden  counterpoise.  Since 
then  there  have  been  no  mishaps.  When  pulled  down 
ready  for  use  the  amblyoscope  hangs  about  3ft.  away  from 
the  wall-bracket  which  supports  the  lighting  apparatus. 


FUSION    TRAINING  I  29 

with  both  hands,  while  I,  putting  my  hands  over 
his,  converge  and  diverge  the  two  halves  of  the 
instrument,  in  order  to  make  the  bird  appear  to  go 
in  and  out  of  the  cage.  Other  similar  pairs  of 
object-slides  are  then  shown.  The  child  soon 
learns  to  move  the  instrument  himself,  so  as  to 
put  the  bird  in  the  cage,  the  cat  on  the  chair,  the 
clown  in  the  hoop,  &c.  One  must  talk  to  the  child 
all  this  time,  as  it  is  only  by  encouraging  him  to 
chatter  that  one  learns  what  he  really  sees. 

A  pair  of  slides  requiring  fusion  of  images  is 
now  shown — fig.  16,  for  example.  The  child  at 
first  sees  two  men,  each  picture  being  imperfect. 
Soon  a  position  is  found  in  which  the  child  sees 
one  man  having  two  legs  and  a  hat.  The  bind- 
ing  screw  in  the  long  slot  is  now  tightened  and 
that  in  the  short  slot  loosened,  so  that  the 
amplitude  of  movement  between  the  two  halves 
of  the  amblyoscope  is  restricted  to  about  io°. 
Other  pairs  of  slides  requiring  fusion  of  images 
are  successively  shown  the  child,  and  he  is  en- 
couraged by  one's  remarks  to  examine  every  part 
of  the  fused  picture.  After  a  time  it  is  found 
that  the  angle  of  convergence  of  the  instrument 
may  be  varied  slightly  without  the  fused  picture 
coming  to  pieces.  The  child  has  now,  under 
these  special  conditions  of  illumination  and  con- 
vergence, the  second  grade  of  binocular  vision, 
— true  fusion  with  some  amplitude. 

The  next  step  is  to  increase  the  amplitude  of 


130  FUSION    TRAINING 

fusion.  The  intensities  of  the  lights  and  the 
angle  of  convergence  of  the  amblyoscope  are 
arranged  as  before.  Devices  requiring  fusion, 
such  as  figs.  16  and  17,  are  shown.  An  attempt 
is  made  to  gradually  diverge  and  converge  the 
two  halves  of  the  instrument,  more  and  more, 
while  the  child  is  examining  and  talking  about 
the  various  pictures  shown  him.  After  some 
practice,  in  the  case  of  a  young  child,  a  con- 
siderable range  of  movement  becomes  possible, 
fusion  being  still  maintained.  This  "amplitude 
of  fusion  "  may,  for  practical  purposes,  be  taken 
as  a  measure  of  the  extent  to  which  the  fusion 
faculty  has  been  developed. 

A  child  who  has  any  considerable  amplitude 
of  fusion  will  nearly  always  be  found  to  have 
acquired  the  third  grade  of  binocular  vision  also 
— the  sense  of  perspective.  The  slides,  fig.  18, 
are  shown,  and  the  child  is  asked  whether  he  is 
looking  at  the  outside  or  the  inside  of  the  tub. 
He  will  at  once  say  "  the  inside."  If  these  slides 
are  now  changed  from  one  tube  to  the  other,  he 
will  see  the  tub  bottom  up. 

The  child  having  now  acquired  the  highest 
grade  of  binocular  vision  under  these  special 
conditions  of  illumination  and  convergence,  the 
next  step  is  to  gradually  equalise  the  light  before 
the  two  eyes.  This  may  readily  be  done,  at  this 
stage,  without  a  return  of  the  suppression. 

If  the  child  be  young  enough,  a  very  powerful 


FUSION    TRAINING  I  3  I 

"desire  for  fusion"  may  usually  be  created  in 
five  or  six  lessons,  given  at  intervals  of  one  week. 

It  must  be  remembered  that  the  prime  object 
of  these  exercises  is  the  training  of  the  fusion 
sense  at  a  time  when  this  may  be  successfully 
accomplished — not  a  mere  remedying  of  the 
deviation.  In  many  cases,  however,  the  powerful 
"  desire  for  fusion  "  thus  established,  directly 
brings  about  a  sudden  cure  of  the  squint.  In  the 
larger  group  of  cases,  in  which  optical  correction 
of  refractive  error  is  depended  upon  to  lessen,  and 
perhaps  overcome,  the  deviation,  there  is  no 
danger  of  the  newly-acquired  faculty  of  fusion 
being  lost  meanwhile.  If  even  a  faint  degree  of 
fusion  sense  has  once  been  acquired,  its  persis- 
tence is  truly  remarkable.  No  matter  how  many 
years  binocular  vision  may  be  in  abeyance,  it 
seems  as  difficult  to  forget  as  the  art  of  swim- 
ming. If  the  periodic  measurements  of  the  angle 
of  the  deviation  show  that  this  is  not  decreasing 
reasonably  quickly  under  optical  treatment,  I  have 
no  hesitation  in  operating  at  any  age,  by  advance- 
ment of  an  external  rectus,  with  or  without  teno- 
tomy of  the  rectus  internus.  The  eye  being  put 
approximately  "straight,"  the  "desire"  for  bi- 
nocular vision  fills  up  any  slight  gap  that  may 
remain,  and  a  perfect  cure  results. 

Fusion  training,  in  the  case  of  these  young 
children,  must  be  carried  out  by  the  surgeon  him- 
self.     It  is  of  no  use  giving  the  amblyoscope,  or 


I32  FUSION    TRAINING 

any  other  instrument,  to  the  mother  for  use  at 
home. 

In  the  case  of  older  children,  I  have  often,  by 
way  of  experiment,  ordered  some  form  of  stereo- 
scope, or  Cuigriet's  (or  Javal's)  "  lecture  con- 
trolee  "  for  home  use.  I  have  not,  in  any  single 
instance,  seen  any  good  result  therefrom.  A 
child  who  is  old  enough  for  "  stereoscopic  exer- 
cises "  and  "bar  reading"  is  far  past  the  age 
when  the  fusion  sense  might  have  been  developed. 
Similarly,  if  he  has  suffered  from  neglected  con- 
stant unilateral  squint  since  infancy,  it  will  now 
almost  certainly  be  impossible  to  remove  the 
acquired  amblyopia  of  the  squinting  eye,  though 
it  might  easily  have  been  done  at  an  earlier  age. 

In  this  description  of  fusion  training  I  wish  to 
draw  attention  rather  to  the  principles  than  to  the 
instruments  by  the  help  of  which  they  have  been 
defined  and  applied.  Though  these  methods 
have  been  constantly  employed  for  many  years, 
it  is  possible  that  they  may  be  improved  upon  ; 
but  the  principles  are  unalterable. 


*33 


CHAPTER  IX. 
DIVERGENT  SQUINT. 

Comitant  divergent  squint  presents  two  distinct 
varieties  differing  widely  in  their  pathology, 
appropriate  treatment  and  prognosis.  They  may 
be  called,  respectively,  myopic  and  neuropathic. 

Myopic  Divergent  Squint. 

The  divergence  most  frequently  first  makes  its 
appearance  at  about  ten  or  twelve  years  of  age. 
It  may  be  either  unilateral  or  alternating,  more 
commonly  the  former.  Usually  the  patient  is 
known  to  have  been  short-sighted  for  four  or  five 
years,  and  the  short-sightedness  has  been  increas- 
ing, until,  at  the  time  of  the  appearance  of  the 
divergence,  there  is  myopia  of  perhaps  5  or  6  d. 
or  more.  As  a  rule  the  fusion  sense  is  well- 
developed,  though  I  have  sometimes  found  it 
deficient.  The  deviation  is  seldom  constant  ; 
at  one  moment  the  eyes  may  be  "  straight "  and 
the  patient  have  binocular  vision  ;  a  few  minutes 
later  one  or  other  eye  may  exhibit  a  high  degree 
of  divergence.  Myopic  divergent  squints  of  low 
degree  are  rare. 
10 


134  DIVERGENT    SQUINT 

From  observing  and  carefully  questioning  many 
of  the  more  intelligent  patients,  I  conclude  that 
the  usual  mode  of  origin  of  a  myopic  divergent 
squint  is  as  follows  : — Soon  after  the  child  begins 
school  it  is  found  that  he  is  not  easily  able  to  see 
the  black-board.  He  is  given  a  front  seat  where 
he  can  see,  and  nothing  more  is  done.  A  few 
years  later,  say  at  twelve  or  thirteen  years  of  age, 
the  myopia  has  increased  so  as  to  bring  his  far 
point  very  near  his  eyes.  All  distant  objects  are 
blurred.  In  reading,  he  has  to  hold  his  book  so 
near  his  eyes  that  it  becomes  very  difficult  to  con- 
verge steadily  to  the  required  extent.  He  com- 
plains that  "the  words  run  into  each  other"  and 
he  soon  tires.  One  frequently  hears  that,  at  about 
this  time,  he  discovered  that,  by  covering  one  eye 
with  his  hand,  he  could  read  quite  comfortably 
with  the  other.  In  any  case,  he  gives  up  the 
struggle  and  allows  one  eye  to  wander  outwards, 
while  he  reads  without  effort  with  the  other.  At 
first  there  is  no  actual  divergence — only  a  failure 
to  converge  while  the  other  eye  is  engaged  in 
near  vision.  But,  as  a  result  of  convergence 
not  being  used,  the  function  becomes  weakened, 
so  that  either  eye  diverges  when  screened  or  when 
the  other  is  being  used  in  near  vision.  When 
the  myopic  eye  has  become  divergent  there  is  no 
diplopia  in  reading,  even  though  the  fusion  faculty 
be  perfect,  because  the  divergent  eye  is  directed 
towards  the    misty  distance.      When  the  patient 


DIVERGENT    SQUINT  I35 

looks  up  from  his  book,  the  divergent  eye  at  first 
always  recovers  itself.  After  a  time,  as  the  habit 
becomes  confirmed,  this  eye  often  remains  widely 
divergent  in  distant  vision.  The  picture  of  distant 
objects  formed  in  the  fixing  eye  is  already  blurred 
and  indistinct,  so  the  very  faint  eccentrically-placed 
image  formed  in  the  divergent  eye  causes  no 
tendency  to  fusion.  But  when  the  divergent  eye 
partially  recovers  its  normal  direction,  so  that  it 
receives  a  more  centrally-placed  image  of  the 
object  to  which  the  fixing  eye  is  directed,  the 
desire  to  blend  these  two  blurred  images  causes 
the  eyes  to  become  straight.  This  probably 
explains  why  in  a  case  of  myopic  divergent  squint, 
the  eyes  are  sometimes  straight,  sometimes  widely 
divergent,  but  scarcely  ever' divergent  to  a  slight 
degree. 

The  treatment  of  a  case  of  myopic  divergent 
squint  consists  in  exactly  correcting  the  myopia 
and  myopic  astigmatism.  The  patient  should 
wear  the  glasses  always,  both  for  near  and  distant 
vision.  Patients  at  first  complain  that  the  glasses 
make  print  appear  very  small.  Children  soon 
become  accustomed  to  them.  But  myopes  who 
first  begin  to  wear  glasses  in  adult  life,  in  some 
cases,  require  a  second  pair  of  glasses  for  near 
vision,  1  d.  or  2  d.  weaker  than  the  distance 
glasses.  Their  power  of  accommodation  has 
become  feeble,  for  want  of  exercise.  Glasses 
with  which  the  patient  can  see  distinctly  usually 


]  $6  DIVERGENT    SQUINT 

cause  a  rapid  disappearance  of  the  squint,  in  fairly 
recent  cases,  and  frequently  even  in  cases  which 
have  lasted  for  many  years.  But  it  often  happens 
that  the  prolonged  disuse  of  the  function  of 
dynamic  convergence  weakens  the  static  conver- 
gence, so  that  this  becomes  a  negative  quantity, 
and  a  tendency  to  divergence  remains.  While 
both  eyes  are  open  and  the  glasses  are  worn,  the 
fusion  faculty  prevents  any  deviation,  but  if  one 
eye  be  shaded  for  a  moment  it  may  diverge  and 
remain  divergent  for  a  second  or  two  after  the 
removal  of  the  shade.  Operation  is  rarely  neces- 
sary. But  in  some  cases,  usually  of  long  standing, 
in  which  the  static  convergence  remains  very 
deficient,  advancement  of  an  internal  rectus  adds 
greatly  to  the  patient's  comfort. 

It  must  not  be  forgotten  that  the  case  may  be 
complicated  by  muscular  exophoria. 

Infantile  myopic  divergent  squint,  excluding 
cases  of  buphthalmos,  is  very  rare.  I  have  notes 
of  only  seven  cases.  These  cases  differed  from 
unilateral  convergent  squints  only  in  the  kind  of 
refractive  error  and  the  direction  of  the  deviation. 
The  treatment  was  similar  to  that  employed  in 
convergent  squint. 

Neuropathic  Divergent  Squint. 
The  divergence  nearly  always  dates  from   in- 
fancy.    It  may  be  constant  or  occasional,  unilateral 
or  alternating.       In  the  constant  cases  there  is  a 


DIVERGENT    SQUINT  137 

total  absence  of  the  fusion  sense.    In  the  occasional 
cases  there  is  a  feeble  degree  of  binocular  vision 
when    the    eyes    are     "straight";    when    an    eye 
diverges  there  is  usually  no  diplopia.    The  refrac- 
tion, as   a   rule,  is  normal.      In  the  constant  uni- 
lateral cases  there    may  be  acquired  amblyopia. 
In  other  cases  the  vision  of  the   eye  is  perfect. 
The  divergence  varies  greatly  in  degree,  even  in 
a  case  in   which   it  is  constantly  present.       The 
power   of  dynamic  convergence  is  deficient.     It 
varies    from    time    to    time    in    an    extraordinary 
manner.     One  day,  perhaps,  the  dynamic  conver- 
gence  may  be  almost   normal  ;  a  few  days  later 
the  most  persevering  efforts  may  fail  to  elicit  the 
slightest    movement    of  convergence.      In    these 
neuropathic    divergent    squints,    the    association 
between     accommodation     and    convergence    is 
usually  very  slight.     One  not  infrequently  sees  a 
patient  who  can  nearly  always  voluntarily  correct 
the  faulty  position  of  his  divergent  eye  without 
much  effort,   but  who  habitually  allows  this  eye 
to  diverge  while  he  is  exercising  say  4  or  5  d.  of 
accommodation  in  near  vision.      In  young  subjects 
the   power  of  rotation  of  each  eye  separately   is 
nearly  always  normal  in  every  direction.      In  long- 
standing cases,  however,  the  power  of  independent 
inward  rotation  is  usually  deficient. 

The  subjects  of  neuropathic  divergence  are 
often  bright,  quick-witted,  intelligent,  but  they  are 
nearly  always  very  "  nervous  "  and  highly  strung. 


138  DIVERGENT    SQUINT 

One  frequently  sees  the  same  ocular  defect  in 
other  members  of  the  family.  A  family  history 
of  epilepsy  or  insanity  is  very  common.  I  find 
neuropathic  divergence  more  common  in  females 
than  in  males,  in  the  proportion  of  about  7  to  2. 

The  treatment  of  neuropathic  divergent  squint 
is  not  satisfactory.  There  is  seldom  any  notable 
refractive  error,  and  when  there  is,  its  correction 
produces  no  effect  upon  the  divergence.  Attempts 
at  fusion  training  nearly  always  fail,  however  early 
the  patient  may  be  seen.  Practically  one's  only 
recourse  is  operation.  One  or  both  internal  recti 
should  be  advanced  (e.g.,  Case  B,  166,  p.  162). 
The  externi  should  be  tenotomised  at  the  same 
time  only  when  the  power  of  abversion  is  dis- 
tinctly greater  than  normal.  If  the  power  of 
adversion  is  very  markedly  deficient,  a  musculo- 
capsular  advancement  should  be  performed.  In 
a  case  in  which  divergence  is  not  constantly 
present  and  in  which  there  is  some  slight  degree 
of  fusion,  advancement  gives  a  satisfactory  result 
(e.g.,  Case  B,  165,  p.  161). 

non-comitant  divergent  squints,  other  than 
Paralytic. 
Divergence  in  extreme  myopia.- — In  cases  ot 
progressive  myopia  of  very  high  degree  it  is  not 
uncommon  to  find  the  visual  axes  divergent. 
These  cases  differ  entirely  from  ordinary  myopic 
divergent  squints.      They  are  non-comitant.     The 


DIVERGENT    SQUINT  I  39 

arcs  of  rotation  of  each  eye  are  subnormal  in  every 
direction.  The  divergence  begins  imperceptibly, 
and  increases  slowly  up  to  about  200.  It  is 
generally  held  that  the  divergence  is  caused 
mechanically,  by  the  egg-shaped  eyes  adapting 
their  long  axes  to  the  divergent  positions  of  the 
orbits.  I  believe  this  explanation  to  be  correct. 
Increased  tension  of  the  external  recti  does  not 
appear  to  be  an  important  factor,  as  I  have,  in 
three  such  cases,  seen  both  these  muscles  teno- 
tomised  without  result. 

Divergence  of  blind  eyes.  —When  both  eyes  are 
blind  they  almost  invariably  diverge.  When  one 
eye  only  is  blind,  its  behaviour  will  depend,  to  a 
great  extent,  upon  the  state  of  the  refraction  of 
the  seeing  eye.  If  this  is  normal  or  myopic  the 
blind  eye  will,  as  a  rule,  diverge ;  if  it  is  markedly 
hypermetropic  it  will  usually  converge. 

If  the  refraction  of  one  eye  be  normal,  or  nearly 
so,  while  the  other  eye  is  very  highly  myopic,  the 
latter  is,  in  the  absence  of  optical  correction, 
practically  a  blind  eye,  and  will  behave  as  such. 

In  a  case  of  convergent  squint  in  which  the 
squinting  eye  has  become  very  amblyopic,  this 
blind  eye  may  become  divergent  in  after  years, 
without  any  tenotomy  having  been  performed. 

Divergence  secondary  to  tenotomy  of  an  internal 
rectus  muscle. — As  already  explained,  in  a  large 
proportion  of  cases  of  convergent  squint  with 
hypermetropia,    the  constant  wearing  of  glasses 


140  DIVERGENT    SQUINT 

gradually  causes  the  visual  axes  to  become  less 
convergent.  It  was  formerly  the  practice  to 
tenotomise  an  internal  rectus  in  almost  all  cases 
of  convergent  squint,  without  going  into  the 
question  of  refractive  error.  Such  of  the  hyper- 
metropes  who  subsequently  took  to  wearing- 
convex  glasses  to  improve  their  vision,  ran  con- 
siderable risk  of  divergence. 

If  tenotomy  be  performed  only  in  cases  in 
which  optical  treatment  has  failed,  the  risk  is 
less.  But  even  then  a  case  of  divergence  will 
occasionally  be  seen.  In  an  ordinary  tenotomy 
the  tendon  and  its  lateral  expansions  are  divided. 
Usually  the  cut  end  of  the  tendon  becomes  con- 
nected to  its  old  insertion  by  an  irregular  band  of 
scar  tissue,  which  may  or  may  not  subsequently 
stretch.  Tenotomy  is  called  a  "  setting  back  "  of 
the  tendon,  because  it  is  supposed  that  the  tendon 
becomes  directly  reattached  to  the  globe  further 
back.  I  believe  that  this  seldom  happens  after  a 
neatly  -  performed  tenotomy.  Sometimes  the 
tendon  fails  to  become  reattached  to  the  globe  at 
all.  In  this  case  the  surgeon  may  fail  to  find  the 
muscle  unless  he  knows  where  to  look  for  it.  Its 
anterior  end  will  be  found  behind  the  sunken 
caruncle,  lying  against  the  inner  wall  of  the  orbit 
(see  page  213). 


I4i 


CHAPTER   X. 

THE    TREATMENT    OF    SQUINT. 
I L  L  USTRA  Tl  I TE  CA  SES. 

The  following  clinical  notes,  copied  from  my 
squint  case-books,  will  serve  to  further  explain 
the  methods  of  treatment  which  I  employ,  and  to 
show  the  results  which  may  ordinarily  be  expected 
therefrom. 

As  a  rule,  it  is  only  possible  to  get  a  perfect 
result  in  a  case  in  which  efficient  treatment  is 
commenced  early.  But,  unfortunately,  one  sees 
a  very  large  proportion  of  the  cases  for  the  first 
time  after  years  of  neglect,  or  perhaps  inadequate 
or  even  harmful  treatment.  I  have,  therefore, 
also  selected  some  examples  of  these  old  cases. 

Case  B,  23.  February  4,  1896.— A  boy,  aged  2  years 
11  months,  was  brought  to  me,  suffering  from  conver- 
gent squint.  He  had  squinted  for  about  ten  or  twelve 
months.  L.  E.  was  convergent  280.  Fixation  was 
present  in  L.  E.,  but  the  sight  of  this  eye  had  de- 
teriorated so  much  that,  when  R.  E.  was  bandaged, 
he  could  not  find  a  white-handled  penknife  on  the 
floor,  unless  it  was  close  to  his  feet.  Abversion  L.  E. 
was  perfect.  Ordered,  atropine  ointment,  1  per  cent., 
thrice  daily  for  both  eyes,  for  retinoscopy. 

February    11. — Convergent    squint    L.    E.    320   with 


142  TREATMENT    OF    SQUINT 

atropine.  Retinoscopy — each  eye  +  275  D.  sph. 
+  0-5  d.  cyl.  ax.  vert.  Ordered  spectacles  +  2*25 
D.  sph.  +  0*5  D.  cyl.  ax.  vert.,  also  guttas  atropine 
1  per  cent,  for  R.  E.  only  every  morning. 

March  3. — Child  uses  R.  E.  (atropised)  in  distant 
vision,  and  L.  E.  (unatropised)  in  near  vision.  Con- 
vergent squint  L.  E.  200,  with  glasses.  Ordered, 
continue. 

April  9. — Similar  note.  Convergent  squint  L.  E. 
1 70.     Ordered,  continue. 

May  29. — Child  now  uses  (unatropised)  L.  E.  and 
turns  in  (atropised)  R.  E.  always,  both  in  near  and 
distant  vision.  Ordered,  stop  the  drops,  and  come 
again  in  one  month. 

June  18. — Squint  nearly  alternating,  slight  prefer- 
ence for  squinting  with  L.  E.  Convergent  squint  L.  E. 
1 6°.  Ordered,  atropine  for  R.  E.  only,  every  morning 
for  a  month,  then  stop  it  and  bring  the  child  to  me 
two  or  three  weeks  later. 

August  4. — C.  S.  alternating  140.  Fusion  training 
with  amblyoscope.  Child  sees  both  images  readily  and 
can  sometimes  blend  them. 

August  7. — Fusion  training. 

August  10. — Fusion  training.  Child  blends  images 
readily. 

August  14. —  Fusion  training.  Child  has  considerable 
amplitude  of  fusion.     C.  S.  alternating  150. 

August  18. — Fusion  training. 

August  25. — No  squint  with  glasses.  The  mother 
says  that  the  eyes  have  been  straight  since  the  last 
lesson,  though  he  lias  turned  the  eye  in,  occasionally, 
for  an  instant. 

November  6. — Child  never  squints  now  with  glasses, 
though  he  occasionally  does  so  without  them,  the 
nurse  says.  No  squint  seen  now  either  with  or  without 
glasses. 

October  8,  1897. — Child  going  on  well.  He  never 
squints  now. 


ILLUSTRATIVE    CASES  I 43 

September  29,  1898. — Spectacles  too  small.  Ordered, 
repeat  them. 

June  13,  190 1. — (Aged  8  years  3  months).  Ordered, 
atropine  for  repetition  of  the  retinoscopy. 

June  20. — Retinoscopy  each  eye  +  2*25  D.  sph. 
+  0-5  D.  cyl.  ax.  vert.  Vision,  each  eye  f.  Ordered, 
spectacles  0*5  D.  lower  than  the  retinoscopy,  with  per- 
mission to  take  them  off  while  playing  games. 

August  19,  1902. — The  boy  has  only  used  his  glasses 
for  school  work  since  last  visit,  and  never  when  out 
of  doors.     He  has  not  been  seen  to  squint  for  years. 

Case  B,  18.  November*],  1895. — A  girl,  aged  2  years 
1  month,  was  brought  to  me,  suffering  from  C.  S.  R.  E. 
330.  She  had  squinted  since  she  had  whooping  cough 
aged  1  year  4  months.  She  had  central  fixation  in 
R.  E.,  but  she  evidently  did  not  see  well  with  it  when 
the  L.  E.  was  tied  up.  Abversion  perfect.  Bright, 
intelligent  girl,  only  child.  Mother  has  C.  S.  R.  E. 
Ordered,  atropine  for  retinoscopy. 

November  13. — Retinoscopy  R.  E.  +  175  D.  sph. 
L.  E.  4-  1-25  D.  sph.  C.  S.  R.  E.  260,  with  atropine. 
Ordered,  spectacles  0*25  D.  less  than  retinoscopy  ;  also 
guttae  atrophias  1  per  cent.,  one  drop  in  L.  E.  only, 
every  morning. 

December  11. — Child  uses  R.  E.  (unatropised)  in 
near  vision,  and  L.  E.  (atropised)  in  distant  vision. 
Ordered,  continue. 

February  6,  1896. — Same.     Ordered,  continue. 

April  2. — Child  uses  R.  E.  (unatropised)  now,  both 
in  near  and  distant  vision,  and  squints  with  atropised 
L.  E.     C.  S.  L.  E.  270.     Ordered,  stop  atropine. 

June  4. — Squint  alternates  220.  Fusion  training 
with  amblyoscope  :  child  readily  sees  both  images,  but 
I  cannot  be  certain  that  she  blends  them. 

June  10. — Fusion  training  :  child  learned  to  blend 
images  quite  easily. 


144  TREATMENT    OF    SQUINT 

June  19. — Fusion  training. 

July  1. — Fusion  training. 

July  7. — Fusion  training.  Child  now  has  an  ampli- 
tude of  fusion,  with  the  amblyoscope,  of  io°  to  150. 
C.  S.  alternating  230.  As  the  fusion  faculty  is  well 
developed  and  the  deviation  is  stationary,  I  advised 
operation,  especially  as,  in  view  of  the  insignificance 
of  the  refractive  error,  spectacles  can  be  dispensed 
with.  The  parents  preferred  to  wait  until  the  child 
was  3  years  old.  Child's  fusion  was  exercised  with 
the  amblyoscope  once  a  month  until 

October  5  (aged  3  years). — C.  S.  alternating  220.  I 
advanced  the  right  external  rectus  muscle,  under 
chloroform.  (I  employed  the  method  described  in 
Chapter  XII.). 

Case  dressed  every  day. 

October  12.     Sutures  removed. 

November?,. — R.  E.  is  not  opened  quite  so  widely  as 
L.  E.,  and  there  is  still  some  redness  of  the  conjunctiva. 
There  is  no  squint  now,  and  the  child  has  perfect 
binocular  vision.  She,  of  course,  has  not  worn  her 
glasses  since  the  operation. 

I  saw  the  little  girl  in  January,  1897,  October,  1897, 
June,  1899,  and  again  on 

November  12,  1902. — I  wrote  and  asked  the  mother 
to  bring  her  to  me.  The  child  is  now  nine  years  old. 
She  has  §  vision,  each  eye,  and  perfect  binocular  vision. 
She  only  dimly  recollects  that  she  ever  had  anything 
the  matter  with  her  eyes. 

Case  B.  192.  November  20,  1899. — A  lady,  aged 
23  years.  History — she  began  to  squint  with  the 
L.  E.  when  she  was  about  1  year  old.  She  was  treated 
from  time  to  time  with  "drops."  At  about  4  years 
of  age  she  was  ordered  glasses.  She  has  worn  glasses 
ever  since.  When  she  was  8  years  old  the  L.  E.,  was 
operated  upon  (tenotomy). 


ILLUSTRATIVE    CASES  I  45 

She  now  has  convergent  squint  L.  E.  i6°  both  with 
and  without  her  glasses.  Vision  of  R.  E.,  with  glasses, 
is  §.  L.  E.  has  lost  central  fixation,  and  with  it  she 
can  just  count  fingers  close  to  her  face.  As  the  result 
of  the  tenotomy,  the  L.  E.  is  prominent  and  the  caruncle 
sunken.  Retinoscopy  under  homatropine — R.  E.  + 
i  D.  cyl.  ax.  vert.,  L.  E.  +  175  D.  cyl.  ax.  700  down 
and  out,  at  approximate  macula.  The  blindness  of 
the  left  eye  is  now,  of  course,  quite  incurable.  She 
wishes  to  have  something  done  to  remove  the  deformity. 

December  5. — I  advanced  the  left  external  rectus 
muscle,  under  cocaine  (by  the  method  described  in 
Chapter  XII.). 

December  20. — There  is  a  little  redness  remaining 
from  the  operation.  The  eyes  are  quite  "  straight," 
and  the  advancement  has  had  the  effect  of  replacing 
the  L.  E.  in  its  proper  position  in  the  orbit.  Ordered, 
rigid  pince-nez  +  1  D.  cyl.  ax.  vert. 

June  14,  190 1. — Eyes  quite  normal  in  appearance, 
both  with  and  without  the  glasses. 

Case  D,  318.  April  13,  1900.— Boy,  aged  1  year 
5  months,  seen  at  Moorfields  Hospital.  The  mother 
said  he  had  measles  in  February  and  he  "  has  squinted 
the  last  few  weeks."  C.  S.  R.  E.  370.  Steady  central 
fixation  R.  E.     Ordered  atropine,  for  retinoscopy. 

April  24. — C.  S.  R.  E.  320  under  atropine.  Retino- 
scopy R.  E.  4-  5-5  D.  sph.  L.  E.  4-  4*5  D.  sph.  Or- 
dered, spectacles  R.  E.  4-  5  D.  L.  E.  4-  4  D.  Guttae 
atrophias  1  per  cent,  to  be  put  in  L.  E.  only  every 
morning. 

May  8. — Child  uses  (unatropised)  R.  E.  and  squints 
(atropised)  L.  E.  always.     Ordered,  stop  drops. 

June  5. — Squint  alternates,  210. 

August  7. — No  squint  while  wearing  glasses.  C.  S. 
R.  E.  about  200  without  glasses. 

September  10,  1901. — Glasses  too  small  now,  repeat 
them. 


I46  TREATMENT    OF    SQUINT 

November  7,  1902. — No  squint  seen  here  either  with 
or  without  glasses.  He  is  said  to  turn  in  R.  E.  some- 
times when  his  glasses  are  taken  off  at  bedtime. 

Case  A.,  489.  May  10,  1900. — Boy,  aged  3  years 
4  months,  seen  at  the  West  Ham  Hospital.  C.  S. 
L.  E.  340.  Fixation  L.  E.  was  lost.  Abversion  L.  E. 
full.  The  mother  said  he  had  "squinted  on  and  off 
for  about  a  year."     Ordered,  atropine  for  retinoscopy. 

May  17. — C.  S.  L.  E.  270  with  atropine.  Retino- 
scopy— R.  E.  4-  375  D.  sph.  +  075  d.  cyl.  ax.  250 
down  and  out.  L.  E.  approximately  the  same.  Or- 
dered, spectacles  for  constant  wear,  R.  E.  4-  3-5  D. 
sph.  4-  075  D.  cyl.  ax.  250  down  and  out.  L.  E.  4- 
3-5  D.  sph.  pro  tern.  :  also  R.  E.  to  be  occluded  by  a 
gauze  pad  secured  by  strapping  plaster,  for  one  month. 

June  14. — Steady  central  fixation  L.  E.  Ordered, 
guttae  atropinae  1  per  cent,  for  R.  E.  only  every  morn- 
ing for  one  month. 

July  12. — Child  now  uses  (atropised)  R.  E.  in  distant 
vision,  and  turns  in  L.  E.  In  near  vision  he  uses 
(unatropised)  L.  E.,  and  turns  in  R.  E.  C.  S.  L.  E. 
230.     Ordered,  continue. 

August  30. — Child  uses  R.  E.  distant  vision  and  L.  E. 
near  vision.  When  glasses  are  taken  off,  he  always 
fixes  with  L.  E.  and  turns  in  the  (atropised)  R.  E. 
Ordered,  continue. 

October  25. — Child  uses  (unatropised)  L.  E.  and  turns 
in  the  (atropised)  R.  E.  always,  both  with  and  without 
the  glasses.  Ordered,  stop  the  atropine  and  return  in 
one  month. 

December  6.— C.  S.  L.  E.  io°.  The  child  uses  L.  E. 
almost  as  readily  as  R.  E.  Fusion  training  with 
amblyoscope. 

December  13. — Fusion  training. 

December  20. — Fusion  training.  Child  blends  images, 
but  with  difficulty. 

January  10,  1901.— Fusion  training. 


ILLUSTRATIVE    CASES  I 47 

'January  24. — Fusion  training.  Images  blended  at 
once.     A  fair  amplitude  of  fusion. 

February  7. — No  squint  with  glasses. 

July  11. — No  squint  with  glasses.  When  glasses 
are  taken  off  the  child  has  no  squint,  as  a  rule  ;  but 
when  he  is  told  to  look  at  a  picture  L.  E.  turns  in 
about  350  to  400,  and  he  says  he  sees  two  books  (he 
volunteered  this  statement  without  any  questioning). 

May  29,  1902. — Child  never  squints  now.  Ordered, 
atropine  for  both  eyes  for  repetition  of  the  retinoscopy. 

June  7. — Retinoscopy,  R.  E.  +  3"5  D.  sph.  +  075 
D.  cyl.  ax.  300  down  and  out.  L.  E.  +  3-5  D.  sph.  +  1 
D.  cyl.  ax.  300  down  and  out.  Vision  with  these  glasses 
R.  E.  I,  L.  E.  f .  Ordered,  spectacles  0*5  D.  less  than 
the  retinoscopy. 

Case  D,  832.  May  6,  1902. — A  boy,  aged  9^  years, 
was  brought  to  the  Royal  London  Ophthalmic  Hos- 
pital, because  he  could  not  see  with  the  right  eye.  The 
father  said  that  the  boy  squinted  when  he  was  teething. 
He  was  taken  to  an  eye  hospital  where  he  was  given 
ointment  (probably  atropine)  for  both  eyes  for  about 
a  year.  At  about  3^  years  of  age  he  was  given  glasses. 
The  glasses  gradually  "  cured  the  squint  but  the  sight 
of  the  eye,  which  used  to  squint,  is  almost  gone." 

The  boy  is  wearing  +  4  D.  sph.  each  eye.  Vision 
with  his  glasses — R.  E.  counts  fingers  at  two  feet, 
L.  E.  §.  Fixation  R.  E.  is,  of  course,  lost.  He  has 
C.  S.  R.  E.  40,  with  his  glasses.  Abversion  R.  E.  full. 
Ordered,  atropine  for  retinoscopy. 

May  9. — Retinoscopy  L.  E.  -f  4  D.  sph.  +  id.  cyl. 
ax.  vert.  R.  E.  approximately  the  same.  Vision  with 
glasses — R.  E.  not  improved,  L.  E.  f.  Ordered,  spec- 
tacles 0*5  D.  less  than  retinoscopy.  The  blindness  is 
now  of  so  long  standing  that  it  would  be  quite  hopeless 
to  attempt  to  restore  the  sight  of  the  R.  E. 

Case  A,  58.     April    23,  1894.     I  saw  a  girl,  aged 


I48  TREATMENT    OF    SQUINT 

2  years  3  months.  Alternating  C.  S.  about  300.  She 
had  squinted  since  early  infancy. 

April  26,  1894. — Retinoscopy  under  atropine. — Each 
eye  4-  1*5  D.  sph.     Ordered,  4-  1*25  D.  sph. 

November  j,  1895. — C.  S.  alternating  320.  Attempted 
fusion  training  with  amblyoscope. 

During  November,  1895,  I  made  six  attempts  to 
train  the  child's  fusion  sense.  Though  she  was  a 
tractable  and  intelligent  child,  I  did  not  succeed  in 
getting  even  simultaneous  perception  of  the  object 
slides.  She  could  see  one  picture  or  the  other,  but 
she  could  not  see  both  together.  (Case  of  essentially 
alternating  squint,  with  total  absence  of  the  fusion 
sense.) 

August,  1900. — The  girl  came  to  me  at  the  West 
Ham  Hospital.  She  has  not  worn  the  glasses  for  two 
or  three  years.  Two  years  ago  she  went  to  another 
hospital,  where  the  right  internal  rectus  muscle  was 
tenotomised.  C.  S.  alternating  190  now.  Vision  fi 
each  eye. 

October,  1900.  I  advanced  the  right  external  rectus 
muscle,  under  cocaine. 

November  8,  1900. — The  eyes  are  "  straight "  and 
normal  in  appearance.  The  vision  of  each  eye  sep- 
arately is  perfect.  But  of  course  she  can  neve: 
have  binocular  vision.     No  glasses  required. 

Juue  12,  1902. — Eyes  normal  in  appearance,  patient 
comfortable. 

Case  B,  3. — May  22,  1893.  I  saw  a  girl,  aged  1  year 
5  months.  She  had  C.  S.  R.  E.  about  350.  She  had 
squinted  for  six  or  seven  months.  R.  E.  has  not  lost 
the  power  of  central  fixation.  Ordered,  atropine  for 
retinoscopy. 

May  25. — Retinoscopy  each  eye  +  4  D.  sph.  Or- 
dered, glasses  each  eye  4-  3'5  £>•  sph. :  also,  gutta* 
atropine  1  per  cent.  L.  E.  only  every  morning. 

June  26,  1893. — Glasses  worn  well.     When  the  child 


ILLUSTRATIVE    CASES  149 

is  induced  to  look  at  anything  close  to  the  eyes,  she 
uses  the  R.  E.  (unatropised)  and  turns  in  the  (atropised) 
L.  E.  At  other  times  she  has  C.  S.  R.  E.  about  300. 
Ordered,  continue  drops  for  L.  E.  only. 

July  28.— Child  uses  L.  E.  (atropised)  in  distant 
vision  and  R.  E.  (unatropised)  in  near  vision.  When 
glasses  are  taken  off,  she  always  uses  R.  E.  and  squints 
with  (atropised)  L.  E.     Ordered,  continue. 

September  5.— Child  always  uses  R.  E.  and  squints 
with  the  (atropised)  L.  E.  both  in  near  and  distant 
vision.     Ordered,  stop  the  atropine. 

April  23,  1894.— C.  S.  nearly  alternating.  More 
often  fixes  with  the  R.  E.,  which  was  at  first  the  squint- 
ing eye.     C.  S.  210. 

November  6th,  1895. — Owing  to  my  absence  abroad 
the  child  was  left  much  longer  than  she  should  have 
been.  C.  S.  L.  E.  130.  Ordered,  atropine  for  repeti- 
tion of  retinoscopy. 

November  13.  Retinoscopy  +  3-5  D.  sph.  +  0-5 
D.  cyl.  ax.  vert,  each  eye.  Ordered,  glasses  0*5  D.  less 
than  the  retinoscopy.  As  the  child  now  squinted 
constantly  with  L.  E.  (the  originally  fixing  eye)  I 
ordered  atropine  to  be  put  in  the  R.  E.  only  every 
morning. 

November  27.— She  uses  R.  E.  (atropised)  in  distant 
vision  and  L.  E.  (unatropised)  in  near  vision.  Ordered, 
continue. 

December  20. — Child  now  uses  L.  E.  almost  always 
in  preference  to  the  (atropised)  R.  E.  Ordered,  stop 
atropine. 

January  15,  1896.— C.  S.  nearly  alternating  n°. 
Fusion  training. 

January  20. — Fusion  training. 

January  27. — Fusion  training.    Child  blends  images. 

February  4. — Fusion  training.  Child  has  some  am- 
plitude of  fusion. 

February  13. — Fusion  training.     Considerable  ampli- 
tude of  fusion. 
11 


15O  TREATMENT    OF    SQUINT 

February  20. — Child  has  frequently  said  that  she 
sees  two  faces,  &c.,  since  last  visit.     Fusion  training. 

February  27. — No  squint. 

June  5. — No  squint  with  glasses.  C.  S.,  with  dip- 
lopia, when  glasses  are  taken  off.  Diplopia  is  so  in- 
tense that  the  little  girl  remarks  it  at  once. 

October  19,  1898. — Glasses  too  small.  Ordered, 
repeat  the  glasses,  with  larger  frames.  The  child  is 
never  seen  now  to  squint.  Vision  R.  E.  £,  L.  E.  (the 
originally  fixing  eye)  §  easily,  |  partly. 

October  24,  1902. — At  my  request,  the  mother  brings 
the  child  (aged  now  9  years  10  months)  to  me  again 
for  examination.  She  has  grade  III.  binocular  vision, 
with  a  good  amplitude  of  fusion.  She  never  squints 
now,  either  with  or  without  her  glasses.  She  must 
always  wear  glasses,  of  course,  on  account  of  her 
refractive  error,  but  I  have  given  her  permission  to 
dispense  with  them  during  her  dancing  lessons  and 
gymnasium  practice. 

CASE  A,  437.  January  18,  1900. — I  saw  a  boy,  aged 
3  years  7  months,  at  the  West  Ham  Hospital.  He 
began  to  squint,  aged  2  years  10  months,  during  con- 
v.ikseence  from  scarlet  fever.  Squint  was  at  first 
occasional.  It  became  constant  after  a  few  weeks. 
C.  S.  R.  E.  420.  Good  fixation  K.  E.  Ivory  ball  test 
shows  that  R.  E.  has  at  least  T'\,  vision.  Ordered, 
atropine  for  retinoscopy. 

January  25.— C.  S.  R.  E.  440  with  atropine.  Re- 
tinoscopy—R.  E.  +  475  !)-  sPh-  +  r75  D-  cyl  ax- 
70"  down  and  in.  L.  E.  +  475  D.  Sph.  +  1  D.  cyl.  ax. 
700  down  and  in.  Ordered,  spectacles  075  n.  less  than 
the  retinoscopy  :  also,  guttae  atropine  L.  E.  only  every 
morning. 

February  8.— The  boy  uses  the  unatropised  R.  E. 
always,  both  in  near  and  distant  vision.  C.  S.  320 
with  glasses.     Ordered,  stop  drops. 

Dining  March  and  April  exereises  with  the  amblyo- 


ILLUSTRATIVE    CASES  1 5  I 

scope  were  carried  out  six  times.  They  resulted  in  a 
fairly  well-developed  fusion  sense  with  an  amplitude 
of  fusion  of  about  io°. 

April  26. — C.  S.  alternating  270. 

June  7. — C.  S.  210.     Fusion  training. 

(In  a  case  in  which  I  have  succeeded  in  developing 
the  fusion  sense,  but  in  which  there  is  still  a  consider- 
able degree  of  deviation,  the  next  step  in  the  treatment 
will  depend  upon  measurements  of  the  angle  of  the 
deviation  at  each  visit.  If  this  is  decreasing  at  a  reason- 
able rate,  the  patient  is  given  fusion  training  once 
every  four  or  five  weeks.  This  is  quite  sufficient  to 
preserve  the  fusion  faculty,  while  optical  treatment  is 
being  tried.  If,  however,  the  improvement  ceases,  so 
that  nothing  more  is  to  be  expected  from  the  wearing 
of  glasses,  operation  becomes  necessary.) 

July  12. — C.  S.  160.     Fusion  training. 

August  16. — C.  S.  120.     Fusion  training. 

September  27.  No  squint  with  glasses.  Good  bin- 
ocular vision.  The  mother  says  that  the  eyes  became 
straight  soon  after  the  last  visit.  He  squints,  some- 
times when  the  glasses  are  off.  When  the  glasses  are 
taken  off  here,  in  the  light  he  does  not  squint  ;  but,  in 
the  dark  room,  he  turns  in  one  or  other  eye  most  of 
the  time. 

July  3,  1902. — The  boy  lost  his  glasses  yesterday. 
There  is  no  squint  in  distant  vision,  even  without  the 
glasses.  But  when  he  is  told  to  pick  out  the  letters 
on  a  card  he  uses  his  L.  E.  and  turns  in  the  R.  E.  to 
an  extreme  degree.  He  then  covers  the  R.  E.  with 
his  hand.     Ordered,  repeat  glasses. 

Case  A,  503.     June  7, 1900. — A  girl,1  aged  5  months, 

1  On  October  23rd,  1902,  a  sister  of  this  patient,  an 
infant  aged  14  weeks,  was  brought  to  me  at  the  West 
Ham  Hospital.  She  had  C.S.L.E.  about  300.  On  October 
30th  retinoscopy  under  atropine  +  6  d.  sph.  each  eye.     I 


152  TREATMENT    OF    SQUINT 

brought  to  me  at  the  West  Ham  Hospital.  She  has 
squinted  constantly  with  the  L.  E.  since  she  was  twelve 
weeks  old.  She  has  C.  S.  L.  E.  about  250,  variable. 
Fixation  lost  L.  E.  Abversion  L.  E.  full.  Ordered, 
continuous  occlusion  R.  E.,  by  a  pad  and  bandage,  for 
fourteen  days  :  also.  ung.  atropinae  1  per  cent,  thrice 
daily,  for  both  eyes,  for  retinoscopy. 

June  21. — Steady  central  fixation  L.  E.  Under 
atropine,  angle  of  squint  varies  from  about  200  to  40°. 
Retinoscopy  R.  E.  +  5-5  D.  sph.,  L.  E.  4-  6-5  D.  sph. 

Ordered,  spectacles,  of  the  pattern  described  on  page 
102.  R.  E.  4-  5  D.,  L.  E.  +  6  d.  Ordered  also,  ung. 
atropinae  1  per  cent.,  to  be  put  into  the  R.  E.  only 
every  morning. 

August  16. — Glasses  worn  well,  child  seems  to  be 
quite  unconscious  of  their  presence.  There  is  no 
squint  in  distant  vision.  When  looking  at  anything 
near  at  hand  the  infant  turns  in  the  R.  E.  (atropiscd). 
Ordered,  stop  the  atropine. 

October  8. — No  deviation  with  glasses.  When  glasses 
are  taken  off  L.  E.  turns  in  to  a  variable  degree — about 
300  usually. 

May  9,  1901. — No  Squint  with  glasses. 

October  3. — Glasses  too  small.     Ordered,  repeat  them. 

August  28,  1902. — Glasses  were  lost  ten  days  ago. 
The  child  is  not  squinting  now,  even  without  the 
glasses.     Ordered,  repeat  the  glasses. 

September  25. — No  squint    with   glasses  or  without 


ordered  +  5^5  D.  and  sunt  her  to  Mr.  Hawes,  of  Leaden- 
hall  Street,  who  fitted  spectacles  of  the  pattern  described 
on  page  105.  When  I  saw  her  on  November  6th  she  had 
had  the  spectacles  two  days.  She  was  wearing  them  quite 
happily.  Atropine  was  used  for  the  fixing  eye  only  until 
the  squint  alternated.  I  last  saw  her  on  June  7th,  1904, 
she  had  no  deviation  while  wearing  the  glasses,  and  prism 
test  in  the  dark  room  showed  that  the  natural  development 
of  binocular  vision  was  proceeding. 


ILLUSTRATIVE    CASES  153 

them.  When  a  lighted  match  was  held  before  the 
child's  eyes  in  the  dark  room,  she  of  course  looked  at 
it.  A  prism,  apex  towards  the  nose,  was  then  slipped 
before  one  eye.  This  eye  was  immediately  seen  to 
make  a  slight  inward  rotation  (in  order  to  blend  the 
images  of  the  light),  showing  that  the  child  had  bin- 
ocular vision. 

(I  do  not  think  that  hypermetropes,  during  the  first 
three  or  four  months  of  life,  as  a  rule  make  any  pro- 
longed effort  of  accommodation  in  the  interests  of 
sharp  vision.  But  some  infants,  this  girl,  for  example, 
evidently  do  so.  The  abnormal  accommodative  effort 
caused  an  abnormal  dynamic  convergence,  which  was 
soon  succeeded  by  a  static  convergence,  before  the 
period  at  which  the  fusion  sense,  normally,  has  made 
much  progress  in  development.  By  giving  her  a  pair 
of  spectacles,  and  so  relieving  the  strain  on  the  accom- 
modation, the  visual  axes  were,  in  the  course  of  four 
or  five  weeks,  brought  back  to  parallelism.  This 
allowed  the  natural  development  of  the  fusion  sense 
to  take  place.  The  child,  in  spite  of  the  high  refractive 
error,  is  perfectly  cured,  whether  she  wears  glasses  or 
not.  Nothing  but  an  actual  muscular  paralysis  will 
ever  make  this  child  squint  again. 

The  case  of  this  child's  sister  is  exactly  similar. 

If  I  had  followed  the  practice  recommended  in  the 
text-books,  of  leaving  the  case  until  the  child  was 
"old  enough  to  wear  glasses,"  she  would  then  have 
had  an  incurable  squint,  and  almost  total  blindness 
of  the  left  eye. 

Case  B,  227. — May  16,  1900.— A  girl,  aged  16  years. 
Her  right  eye  is  nearly  blind.  It  turns  out  and  down, 
and  is  very  prominent — a  hideous  deformity— the  result 
of  two  tenotomies  six  years  ago. 

History.— She  had  whooping-cough  soon  after  she 
was  one  year  old.  During  convalescence  the  R.  E. 
turned  in  towards   the    nose.     She    was   taken   to   an 


154  TREATMENT    OF    SQUINT 

ophthalmic  surgeon  at  once.  Being  considered  to  be 
too  young  for  glasses,  she  was  ordered  atropine  drops 
for  both  eyes.  The  drops  were  used  for  both  eyes,  for 
from  a  year  and  a  half  to  two  years.  (How  often  one 
hears  this  disastrous  tale  !)  Soon  after  she  was  three 
years  old  she  was  ordered  spectacles.  At  the  age  of 
10  years,  the  right  eye  was  operated  upon,  in  London 
(tenotomy  of  internal  rectus).  A  year  later  this  eye 
was  again  operated  upon  in  Germany.  After  the 
second  operation  the  R.  E.  was  "  straight."  Soon 
after  that  it  began  to  turn  out  and  down.  This  de- 
formity has  gradually  got  worse. 

At  present  R.  E.  is  very  prominent  :  it  turns  out 
28°  and  down  10".  With  this  eye  she  can  just  dis- 
tinguish hand  movements  close  to  the  face.  Power 
of  adversion  R.  E.  is  absent.  She  is  wearing  spectacles 
+  175  D.  sph.  each  eye.  Vision  L.  E.  |  both  with 
and  without  glasses.  Retinoscopy — with  homatropine 
L.  E.  +  2-25  D.,  R.  E.  +  3*5  D.  at  approximate 
macula. 

Of  course,  the  blindness  of  the  R.  E.  is  now  quite 
incurable.  With  a  view  to  remedying  the  deformity, 
1  advised  that  the  divergence  should  be  dealt  with  by 
operation  first,  and  the  vertical  deviation  at  a  subse- 
quent operation. 

May  21. — Having  cocainised  the  eye,  I  stripped  up 
from  the  globe  the  membranes  on  the  nasal  side,  from 
near  the  edge  of  the  cornea  to  the  sunken  caruncle. 
1  found  the  internal  rectus  muscle  behind  the  sunken 
caruncle,  near  the  inner  wall  of  the  orbit.  It  was  not 
attached  to  the  globe  in  any  way.  As  the  muscle  was 
much  wasted,  I  decided  to  advance  the  conjunctiva, 
and  capsule  of  Tenon  also.  1  seized  all  these  struc- 
tures with  forceps,  and  drew  them  between  the  jaws 
of  a  Prince's  advancement  forceps.  1  secured  these- 
structures,  by  my  usual  method,  to  the  circum-corneal 
fibrous  tissue,  bringing  the  eye  into  a  position  of  very 
slight  convergence. 


ILLUSTRATIVE    CASES  155 

june  16.— I  advanced  the  right  superior  rectus 
muscle. 

june  30.— There  is  still  some  redness  of  the  eye. 
The  advancements  have  drawn  back  the  eye  into  its 
proper  position  in  the  orbit.  In  ordinary  directions 
of  the  gaze  the  eyes  appear  quite  straight.  But,  when 
the  patient  looks  more  than  about  150  to  the  right, 
the  right  eye  ceases  to  follow  the  movement  of  the 
left.  This  is  because,  owing  to  the  wasted  condition 
of  the  internal  rectus  muscle,  1  did  not  dare  to  rely 
upon  the  muscle  alone,  but  was  compelled  to  advance 
the  membranes  also.  But  it  is  easy  for  the  patient  to 
conceal  this  defect,  by  avoiding  wide  excursions  of 
the  eyes.     I  ordered  pince-nez  +  2  D.  sph. 

July  5,  1902. — Patient  does  not  wear  her  glasses  out 
of  doors.  She  always  wears  them  indoors.  The  eyes 
are  quite  natural  in  appearance. 

Case  d,  Si.  September  27,  1S99 .— Boy,  aged  6  years 
5  months,  seen  at  Moorfields.  C.  S.  L.  E.  270.  Ab- 
version  D.  E.  very  slightly  deficient.  He  began  to 
squint  during  convalescence  from  measles,  aged  2\ 
years.  He  has  had  no  treatment.  Ordered,  atropine 
for  retinoscopy. 

September  30.— Retinoscopy  each  eye  +  3  D.  sph. 
4-  075  D.  cyl.  ax.  vert.  Vision  R.  E.  -£,  L.  E.  /«. 
Ordered,  spectacles  0*5  D.  less  than  the  retinoscopy  : 
also,  gutta3  atropine  1  per  cent,  every  morning  R.  E. 
only. 

November  4. — Boy  uses  R.  E.  (atropised)  in  distant 
vision  and  L.  E.  (unatropised)  in  near  vision.  C.  S. 
L.  E.  1 6°.  V.  L.  E.  TV  Ordered,  continue  drops 
R.  E.  only. 

January  3,  1900.— C.  S.  L.  E.  ii°.  V.  L.  E.  T% 
partly.  Boy  too  old  for  fusion  training.  Ordered, 
continue  for  four  months. 

May  2.— C.  S.  L.  E.  6°.  V.  L.  E.  T%  partly.  Or- 
dered, continue  drops  for  R.  E.  for  two  months  more. 


1  56  TREATMENT    OF    SQUINT 

July  4.-C.  S.  L.  E.  50.  V.  L.  E.  &  partly.  Or- 
dered, stop  drops. 

February  6,  1901. — With  the  glasses  there  is  no 
apparent  squint,  but  the  mirror  test  reveals  a  con- 
vergent squint  of  20.  C.  S.  about  150  when  the  glasses 
are  taken  off.     V.  R.  E.  f.,  L.  E.  &  partly. 

Case  D,  734.  November  29,  1901. — Girl,  aged  4 
years  8  months.  C.  S.  R.  E.  220.  Abversion  perfect. 
The  power  of  central  fixation  of  R.  E.  is  lost.  The 
eye  is  so  blind  that,  when  the  good  eye  is  tied  up,  she 
is  unable  to  see  a  penny  on  the  floor  at  her  feet.  She 
hears  it  drop,  and  goes  down  on  her  knees  to  feel  for 
it.     The  mother  says  that  the  squint  began  at  about 

2  years  of  age,  during  an  attack  of  scarlet  fever.  She 
says  she  repeatedly  spoke  to  the  doctor  about  it,  but 
he  told  her  to  "  wait  to  see  if  the  child  would  grow  out 
of  the  squint  !  "     Ordered,  atropine  for  retinoscopy. 

December  3. — C.  S.  R.  E.  260  with  atropine.  Retino- 
scopy R.  E.  4-  3  D.  sph.  at  approximate  macula.  L.  E. 
+  3  D.  sph.  Ordered,  spectacles  +  2*5  d.  sph.  each 
eye  :  also  L.  E.  to  be  continuously  occluded  by  a 
gauze  pad  and  strapping. 

January  3,  1902. — When  the  eye  was  at  first  tied 
up,  she  used  to  fall  over  things,  the  mother  says.  Later, 
she  could  see  to  run  about  very  well.  Child  has  now 
central  fixation  R.  E.  Ordered,  discontinue  pad  ; 
guttae  atrophia.'  1  per  cent,  to  be  put  into  L.  E.  only, 
every  morning.  Child  to  go  to  school  and  use  the  eyes 
in  near  vision  as  much  as  possible. 

February  6. — Child  uses  (atropised)  L.  E.  in  distant 
vision,  and  (unatropised)  R.  E.  111  near  vision.  Ordered, 
continue  atropine  L.  E.  only. 

May  2. — With  glasses  child  uses  (atropised)  L.  E. 
in  distant  vision,  and  (unatropised)  R.  E.  in  near  vision. 
When  the  glasses  air  off  she  ums  the  l\.  E.  and  turns 
in  L.  E.  always.  C.  S.  R.  E.  [6°  with  glasses.  Or- 
dered, continue  atropine  L.  E. 


ILLUSTRATIVE    (ASKS  157 

October  3.— Vision  R.  E.  with  glasses  T%  easily.  C.  S. 
R.  E.  13°.     Ordered,  continue  atropine  L.  E.  only. 

December  2. — Child  uses  (unatropised)  R.  E.  now 
always,  both  in  near  and  distant  vision,  and  turns  in 
the  (atropised)  L.  E.  C.  S.  L.  E.  140.  Vision  R.  E. 
I  with  difficulty  ;  f  easily  ;   L.  E.  f . 

(In  private  practice,  I  should  have  aimed  at  a  per- 
fect cure  of  the  squint,  by  training  the  fusion  sense. 
But,  in  a  crowded  hospital  clinic,  it  is,  unfortunately, 
not  possible  to  find  time  for  fusion  training,  except 
in  a  very  small  proportion  of  the  cases.  But  it  is 
something  to  have  restored  the  sight  of  the  blind  eye.) 

Case  A,  541.  August  9,  1900.— A  boy,  aged  16  years, 
came  to  me  at  West  Ham  Hospital.  He  had  squinted 
with  L.  E.  since  infancy.  He  had  worn  glasses  since 
he  was  4  years  old.  He  was  wearing  4-  3*5  D-  sPh- 
each  eye.  Vision  with  glasses,  R.  E.  f,  L.  E.  fo  He 
had  C.  S.  L.  E.  n°,  with  his  glasses.  His  glasses  were 
found  to  be  suitable.  Adversion  L.  E.  good.  Dynamic 
convergence  good.  It  was,  of  course,  much  too  late 
to  attempt  to  restore  the  sight  of  the  left  eye.  He 
wished  to  have  the  deformity  removed. 

Under  cocaine  and  supra-renal  extract,  I  performed 
complete  central  tenotomy  of  left  internal  rectus  by 
the  method  described  on  page  216. 

August  16. — Scarcely  any  redness  remaining.  C.  S. 
L.  E.  30,  with  his  glasses.  This  small  squint  is  quite 
masked  by  the  angle  gamma. 

May  8,  1902.— Patient  has,  with  his  glasses,  C.  S. 
L.  E.  40.     There  is  no  noticeable  deformity. 

Case  B,  19.  November  12,  1895.— A  girl,  aged 
3  years  1  month.  She  began  to  squint  during  con- 
valescence from  measles,  aged  1  year  10  months. 
Squint  was,  at  first,  occasional.  It  soon  became  con- 
stant. She  has  now  C.  S.  alternating  360.  Ordered, 
atropine  for  retinoscopy. 


158  TREATMENT    OF    SQUINT 

November  16. — C.  S.  alternating  320,  with  atropine. 
Ketinoscopy,  each  eye,  +  5  D.  sph.  +  1  D.  cyl.  ax. 
vert.  Ordered,  glasses  +  4 '5  D.  sph.  +  i  D.  cyl.  ax. 
vert. 

November  27. — C.  S.  alternating  280,  with  glasses. 
Fusion  training  with  amblyoscope. 

December  5.—  Fusion  training.  Child  easily  fuses 
images. 

December  18. — Fusion  training. 

January  10,  1896. — Fusion  training.  Child  has  an 
amplitude  of  fusion  of  at  least  io°.  C.  S.  180  with 
glasses. 

January  18. — Fusion  training. 

February  12. — Fusion  training.  Child  can  follow  the 
images  through  a  range  of   150  or  200.     C.  S.  120. 

March  11. — Fusion  training.     C.  S.  io°. 

March  30. — No  squint  with  glasses. 

October  8. — No  squint.     Glasses  worn  comfortably. 

August  21,  1897. — Child  never  squints  now.  Or- 
dered, similar  glasses  in  larger  frames. 

July  7,  1899.  The  girl  never  squints  now,  even  when 
the  glasses  are  taken  off ;  but  she  must,  of  course, 
continue  to  wear  the  glasses  on  account  of  her  high 
refractive  error. 

CASE  B,  II.,  57.  January  13,  1902.  A  girl,  aged 
1 1  years  5  months.  Histoty.  She  began  to  squint 
with  L.  E.  when  she  was  6  years  old.  She  has  squinted 
with  this  eye  constantly  ever  since.  When  she  was 
about  8  years  old  she  had  glasses.  In  April,  1899,  the 
left  internal  rectus  muscle  was  tenotomised,  and  in 
June,   1899,  the  right   also. 

She  now  has  convergent  squint  L.  E.  15°,  with  the 
glasses.  Her  vision,  with  her  glasses,  is  g  each  eye. 
She  has  a  faint  homonymous  diplopia  when  she  looks 
for  it.  On  examining  her  fusion  sense  with  the  am- 
blyoscope she  readily  blends  images,  but  has  almost 
no  amplitude  of  fusion. 


ILLUSTRATIVE    CASES  159 

January  24.— Retinoscopy  under  atropine,  each  eye, 
+  3-5  D.  sph.  +  1-5  D.  cyl.  ax.  300  down  and  out.  This 
very  nearly  corresponds  with  the  glasses  she  has  been 
wearing. 

February  12. —By  my  direction,  the  glasses  have 
been  left  off  for  the  last  twenty-four  hours.  Without 
glasses,  R.  E.  fixing,  the  deviation  is  220.  L.  E.  fixing, 
the  deviation  is  350.  (Approximate  estimation  by 
mirror  test). 

I  advanced  the  left  external  rectus  muscle  (under 
cocaine),  of  course  without  tenotomising  the  internal 
rectus.     Eyes  "  straight  "  after  operation. 

February  19. — Removed  sutures.  Mirror  test  shows 
binocular  fixation. 

February  28.— The  patient  had  binocular  vision, 
both  with  and  without  her  glasses,  but  the  amplitude 
of  fusion  is  very  small. 

June  18.— Since  the  operation  I  have,  by  way  of 
experiment,  attempted  to  increase  the  amplitude  of 
fusion,  but  of  course  without  success.  She  has  now 
just  the  same  small  degree  of  fusion  sense  which  she 
had  when  she  began  to  squint,  and  which  she  has 
had  ever  since — neither  more  nor  less.  But  an  accu- 
rately performed  advancement  has  enabled  her  to  use 
this  feeble  fusion  sense.  The  eyes  are  exactly  straight 
and  the  child  has  binocular  vision. 

The  reason  of  the  good  vision  in  the  deviating  eye 
is  the  unusually  late  onset  of  the  deviation.  Am- 
blyopia from  disuse  is  scarcely  ever  acquired  after  six 
years  of  age. 

Case  B,  33.  May  5,  1896.— Boy,  aged  2  years 
7  months.  The  right  eye  turned  in  suddenly  a  little 
before  he  was  two  years  old.  He  has  squinted  con- 
stantly ever  since.  C.  S.  R.  E.  270.  Central  fixation 
R.  E.  With  R.  E.  he  can  with  difficulty  see  the  i|  inch 
ivory  ball  at  four  yards.  Abversion  each  eye  perfect. 
Ordered,  atropine  for  retinoscopy. 


l6o  TREATMENT    OF    SQUINT 

May  12. — Under  atropine  C.  S.  R.  E.  30".  Retino- 
scopy,  each  eye  +  2*25  D.  sph.  Ordered,  spectacles 
+  2  D.  sph.  constant  wear  :  also  guttae  atrophia?  1  per 
cent.  L.  E.  only,  every  morning. 

July  3. — Child  uses  the  R.  E.  (unatropised)  in  neat- 
vision  and  the  L.  E.  (atropised)  in  distant  vision.  C.  S. 
R.  E.  210  with  glasses.     Ordered,  continue. 

August  26. — Same.  C.  S.  R.  E.  180.  Ordered,  con- 
tinue. 

October  12. — The  boy  uses  the  (unatropised)  R.  E.„ 
and  turns  in  the  (atropised)  L.  E.,  nearly  always  now, 
even  in  distant  vision.     Ordered,  continue. 

November  6. — C.  S.  L.  E.  always  now  120.  Ordered, 
stop  atropine. 

November  27. — Squint  alternates  now  o°.  Fusion 
training  with  amblyoscope. 

December  4. — Fusion  training.  Child  readily  blends 
images,  but  he  has  at  present  no  amplitude  of 
fusion. 

December  10. — Fusion  training. 

December  14. — Fusion  training. 

December  16. — Fusion  training. 

December  19. — Fusion  training.  Good  amplitude  of 
fusion. 

January  22,  1897. — No  squint. 

August  12. — Child  wears  his  glasses.      No  squint. 

October  25,  1898. — Child   never  squints  now. 

July  18,  1899 — The  boy  does  not  squint  even  when 
tlie  -lasses  are  taken  oil. 

June  13,  1902. — Ordered,  atropine  for  retinoseopv. 

June  18.— Retinoseopv  R.  E.  +  175  I),  sph.  +  0*25 
D.  cyl.,  L.  E.  +  175  i).  sph.  Vision  ;;  each  eve. 
Ordered,  glasses  for  near  work  +  175  D.  sph.  No 
glasses  to  be  worn  out  of  sehool.  To  be  seen  again  in 
three  months. 

September  22. — The  boy  gets  on  well  without  glasses. 
He  prefers  not  to  use  them  even  for  sehool  work.  He 
never  squints  now. 


ILLUSTRATIVE    CASES  l6l 

Case  B.,  165.  July  19,  1899.— Girl,  aged  3  years 
5  months.  Since  earliest  infancy  R.  E.  had  turned 
out  occasionally  :  worse  during  the  last  year.  Never 
any  diplopia.     Always  a  delicate  and  timid  child. 

The  eyes  sometimes  fix  hinocularly,  but  more  often 
R.  E.  is  widely  divergent.  When  the  child  is  spoken 
to  the  eyes  recover  their  normal  relative  directions 
immediately,  but  when  she  looks  at  a  near  object  the 
R.  E.  is  usually  allowed  to  diverge.  Dynamic  con- 
vergence very  deficient.  All  separate  movements  of 
each  eye  perfect.  With  L.  E.  the  child  easily  sees 
the  ^  inch  ivory  ball  at  six  yards.  With  R.  E.  she  can 
with  difficulty  see  the  1^  inch  ball  at  three  yards. 
R.  E.  has  not  lost  central  fixation.  Amblyoscope  test 
shows  that  the  child  has  some  slight  degree  of  fusion 
sense. 

July  26. — Retinoscopy  under  atropine,  each  eye  + 
1*25  D.  sph.  No  glasses  ordered.  Ordered,  guttae 
atrophias  sulph.  1  per  cent.  L.  E.  only  every  morning. 

August  22. — Child  now  uses  L.  E.  (atropised)  for 
distance,  and  R.  E.  (unatropised)  in  near  vision. 
Ordered,  continue. 

October  27. — Child  uses  R.  E.  in  near  vision  and 
sometimes  in  distant  vision  also.  WTith  R.  E.  she  can 
easily  see  the  f  inch  ivory  ball  at  six  yards.  Ordered, 
atropine  L.  E.  only  every  morning,  first  seven  days  in 
each  month,  for  six  months. 

September  20,  1900. — Divergence  is  nearly  alternating. 
Still  some  preference  for  fixing  with  L.  E. 

July  16,  1902. — Divergence  almost  always  present 
now.     V.  R.  E.  -I  partly,  V.  L.  E.  f. 

July  29. — Advancement  R.  internal  rectus  muscle, 
under  cocaine.  Patient  kept  in  bed  with  both  eyes 
bandaged  for  one  week  after.  Stitches  then  removed. 
Two  days  later  all  dressings  discontinued. 

August  26. — Eyes  "straight."  Child  blends  images 
except  on  looking  to  extreme  R. 

(The  feeble  degree  of  fusion  sense  which  developed 


1 62  TREATMENT    OF    SQUINT 

in  early  childhood  was  nut  sufficient  to  prevent  the 
deviation,  or  even  to  cause  diplopia,  but  now  that  the 
deviation  has  been  overcome  by  operation  it  enables 
her  to  fuse  the  two  images.) 

Case  B,  166.  July  19,  1899. — Girl,  aged  8  years  2 
months,  sister  of  the  preceding  case.  Alternating 
divergent  squint  of  variable  degree,  usually  about  350. 
Association  between  accommodation  and  convergence 
almost  absent.  Separate  movements  each  eye  normal, 
except  adversion,  which  is  slightly  deficient.  Fusion 
sense  absent.  H.m.  0-5  D.  No  As.  V.  each  eye  f. 
Child  has  worn  spectacles  +  075  D.  sph.  for  about 
three  years.  Recommended  advancement  of  one  or 
both  internal  recti  for  cosmetic  reasons.  No  glasses 
required. 

August  22. — Advancement  R.  internal  rectus,  under 
cocaine  (of  course  without  tenotomy  of  externus.) 

November  8. — Advancement  L.  internal  rectus. 

December  20. — No  noticeable  deformity  now.  Eyes 
appear  to  be  quite  normally  directed.  Mirror  test, 
however,  shows  that  there  is  sometimes  slight  diverg- 
ence and  sometimes  slight  convergence.  Of  course 
there  is  no  fusion  :  she  really  uses  the  eyes  alternately, 
although  she  appears  to  use  them  together. 

October  5,  1904. — Condition  as  at  last  visit  five  years 
ago. 

Casio  A,  79.  December  5,  [895.  Girl,  aged  16  years. 
Eyes  are  already  under  atropine.  L.  E.  is  widely 
divergent.  When  told  to  look  at  a  near  object  she  can, 
by  an  effort,  overcome  the  deviation,  but  the  eye  soon 
diverges  again.  Adversion  slightly  deficient.  Patient  is 
known  to  have  been  "short-sighted  for  some  years; 
getting  worse."  Four  or  five  years  ago  L.  E.  turned 
out,  occasionally  at  first,  but  during  the  last  year 
constantly.  She  often  sees  double.  Small  myopic 
crescent  each  eve.     Choroidal  vessels  seen.     Retino- 


ILLUSTRATIVE    CASES  I  63 

scopy  R.   E.  —  6-5  I),  spli.     V.    |    partly.     L.   E.   - 
6*5  D.  sph.   —    175   D.   cyl.    ax.    150    down    and    out. 
V.   f.      Ordered,    full    correction    to     be    worn    con- 
stantly. 

February  13,  1896. — When  she  Hrst  began  to  wear 
the  glasses  they  made  her  head  ache,  but  she  soon 
became  accustomed  to  them.  Now  she  finds  them 
quite  comfortable.  No  divergence  now.  When  she 
is  tired  she  "  squints  and  sees  double  for  a  moment 
until  the  eyes  come  straight  again."  While  wearing 
the  glasses  either  eye  diverges  when  screened,  about 
200. 

October  8. — Glasses  very  comfortable.  No  headaches. 
No  divergence.  Behind  Maddox  rod  either  eye  turns 
out  120,  varies  slightly. 

September  23,  1897. — Retinoscopy  under  atropine 
shows  that  the  myopia  has  increased  075  D.  Ordered, 
continue  same  glasses. 

July  20,  1899.  She  is  never  seen  to  squint,  but 
says  that  she  occasionally  sees  double  for  a  moment. 
Behind  Maddox  rod  either  eye  diverges  8°  or  90. 

July  27.  Retinoscopy  under  atropine.  R.  E.  — 
7-5  D.  sph.  V.  §  L.  E.  -  75  D.  sph.  -  175  D.  cyl. 
ax.  120  down  and  out.  V.  f.  Ordered,  full  correction, 
to  be  worn  constantly. 

August  20,  1903. — Eyes  comfortable.  Never  any 
divergence.     Exophoria  is  now  only  20. 

August  27. — Retinoscopy  under  atropine  shows  that 
the  myopia  has  increased  less  than  0-5  D.  during  the 
last  four  years. 


,64 


CHAPTER    XI 
HETEROPHORIA. 

If  a  person,  with  a  perfectly  normal  pair  of 
eyes,  looks  steadily  at  any  object,  both  visual 
axes  will  continue  to  be  accurately  directed  to 
that  object,  even  though  one  eye  be  shaded.  1  n 
other  words,  his  perfectly  balanced  motor  coordi- 
nations are  able  to  maintain  the  normal  relative 
directions  of  the  eyes,  even  when  the  controlling 
influence  of  the  fusion  sense  is  temporarily  with- 
drawn. This  state  of  perfect  oculo-motor  equi- 
librium is  called  orthophoria. 

Heterophoria  is  the  name  given  to  the  con- 
dition of  imperfect  oculo-motor  balance.  There 
is  here  a  tendency  for  the  eyes  to  deviate  from 
their  normal  relative  directions.  Ordinarily,  how- 
ever, this  tendency  is  kept  in  check  by  the  fusion 
sense,  so  that  there  is  no  squint.  But  if  binocular 
vision  be  temporarily  rendered  impossible — e.g., 
by  covering  one  eye — this  tendency  gives  rise  to 
an  actual  deviation. 

Heterophoria  of  sufficient  degree  to  cause 
trouble  is  not  very  common.  Of  those  who  suffer 
from  "asthenopic  symptoms,"  in  only  a  very 
small  proportion  of  cases  are  the  symptoms  found 


HETEROPHORIA.  1 65 

to  be  due  to  heterophoria.  Occasionally,  how- 
ever, one  meets  with  a  patient  who  complains  of 
pain  and  discomfort  in  the  eyes,  and  whose  refrac- 
tion has  been  repeatedly  examined,  and  who  has 
for  years  worn  glasses  to  correct  some  unim- 
portant refractive  error,  without  any  relief  to  his 
suffering.  Such  a  patient  usually  has  a  hetero- 
phoria, the  correction  of  which  immediately  and 
permanently  removes  his  trouble. 

Heterophoria  may  perhaps  be  due  to  a  muscle 
or  group  of  muscles  being  too  weak  or  too  strong 
for  the  opponents,  or  to  an  abnormal  position  of 
insertion  of  a  tendon,  whereby  the  muscle  acts  at 
less  or  more  than  its  normal  mechanical  advan- 
tage, or  to  a  muscle  or  group  of  muscles  being 
too  feebly,  or  too  powerfully,  innervated.  As  a 
rule,  we  are  unable  to  determine  whether  the  fault 
lies  in  the  muscles  themselves,  or  in  their  innerva- 
tions. We  can  only  say  that  certain  actions  are 
deficient  or  excessive.  Heterophoria  is  essen- 
tially a  motor  anomaly. 

Squint,  on  the  other  hand,  is  essentially  due 
to  a  defect  of  the  fusion  faculty.  In  the  presence 
of  this  fundamental  cjiuse,  heterophoria  may  give 
rise  to  a  permanent  squint  with  suppression  of  one 
image  :  not  otherwise. 

There  is  an  apparent  exception  to  this  rule — a 
person  who  has  previously  enjoyed  perfect  bino- 
cular vision  may  have  the  visual  acuity  of  one 
eye  so  lowered  by  progressive  myopia,  injury,  or 
12 


I  66  HETEROPIIORIA 

disease  as  to  render  binocular  vision  impossible. 
Any  heterophoria  which  may  be  present  will  then 
cause  a  manifest  squint,  although  the  cerebral 
faculty  of  fusion  remains  perfect. 

Heterophoria  is  the  generic  name,  invented  by 
Stevens,  for  all  latent  tendencies  to  deviation. 
Distinctive  names  are  employed  to  indicate  the 
direction  of  the  tendency  : — 

Esophoria  is  a  tendency  to  abnormal  static 
convergence  of  the  visual  axes. 

Exophoria  is  a  tendency  to  divergence  of  the 
visual  axes. 

Hyperphoria  is  a  tendency  of  the  two  eyes  to 
rotate  vertically  in  opposite  directions,  so  that 
one  visual  axis  shall  lie  in  a  higher  plane  than 
the  other.  The  eye  which  tends  to  turn  upwards 
is  called  the  hyperphoric  eye. 

Cyclophoria  is  a  tendency  to  abnormal  rotation 
of  one  or  both  eyes  round  a  fore-and-aft  axis,  so 
that  what  should  be  the  vertical  meridian  of  the 
eye  shall  be  no  longer  parallel  to  the  median 
plane  of  the  head.  A  tendency  for  the  vertical 
meridian  of  the  eye  to  lean  away  from  the  median 
plane  is  called  plus  cyclophoria.  A  tendency  in 
the  opposite  direction  is  called  minus  cyclophoria. 

Pseudo-heterophoria. — In  a  case  of  uncorrected 
ametropia  there  is  frequently  an  apparent  hetero- 
phoria which  disappears  when  the  appropriate 
correcting  glasses  are  worn.  The  term  hetero- 
phoria should  be  reserved  for  cases  in  which  the 


HETEROPHORIA  \6j 

anomaly  persists  after  optical  correction  of  any 
refractive  error  which  may  be  present. 

If  the  patient  be  ametropic,  he  should  wear  an 
exact  correction  of  his  ametropia  during  the  ex- 
amination. But  this  spurious  heterophoria  does 
not  always  disappear  immediately  on  correcting 
the  refractive  error.  So  that,  if  the  latter  be  con- 
siderable, one  should  not  immediately  conclude 
that  any  heterophoria  which  may  be  found  is 
genuine.  The  results  should  be  checked  by  a 
second  examination  after  glasses  correcting  the 
refractive  error  have  been  worn  for  several  weeks. 

The  symptoms  of  heterophoria  are  those  of 
"  eye-strain  "  in  general — frontal  headache  coming 
on  towards  the  end  of  the  day  ;  pain  in  the  eyes 
after  watching  anything  intently,  e.g.,  a  play  ;  mi- 
graine ;  dizziness  (especially  associated  with  hy- 
perphoria) ;  conjunctival  hyperemia,  &c.  In  the 
higher  degrees  of  heterophoria  momentary  de- 
viation with  diplopia  is  not  uncommon. 

Asthenopic  symptoms,  which  do  not  yield  to 
accurate  optical  correction  of  any  refractive  error 
which  may  be  present,  should  always  lead  to 
investigation  of  the  motor  balance  of  the  eyes,  if 
this  has  not  already  taken  place. 

People  vary  greatly  in  their  susceptibility  to 
suffering  as  the  result  of  heterophoria,  just  as 
they  do  in  the  case  of  refractive  error.  Other 
things  being  equal,  hyperphoria  is  the  form  of 
heterophoria  which  is  most  likely  to  cause  trouble, 


l68  HETEROPHORIA 

and  esophoria  the  least.  It  is  not  uncommon  to 
see  a  patient  who  has  several  degrees  of  eso- 
phoria, and  who  is  quite  unconscious  of  any  defect ; 
whereas  few  men  can  support  a  hyperphoria  of 
more  than  one  degree  without  inconvenience. 

The  importance  of  a  case  of  heterophoria  is 
proportionate  to  the  trouble  which  it  causes.  A 
case  which  gives  rise  to  no  symptoms  requires  no 
treatment. 

Heterotropia. — A  person  whose  fusion  sense 
has  developed  perfectly,  but  who  has  a  very  high 
degree  of  heterophoria,  will  be  able  (with  more 
or  less  suffering)  to  keep  this  deviation-tendency 
in  check  during  the  adaptable  and  vigorous 
period  of  childhood  and  youth,  but,  when  he 
exchanges  school  life  for  some  more  trying  and 
less  healthy  occupation,  he  may  find  himself 
unable  to  continue  the  struggle,  in  which  event 
his  heterophoria  gives  rise  to  an  actual  deviation. 
He  then  loses  his  asthenopic  symptoms,  but  he 
suffers  from  diplopia,  which  is  usually  so  annoy- 
ing that  he  is  glad  to  shade  or  close  one  eye. 
The  degree  of  the  manifest  deviation  increases 
during  the  first  few  weeks  or  months,  after  which 
it  becomes  stationary.  The  term  heterotropia 
should  be  reserved  for  this  rather  rare  condition, 
as  it  is  obviously  a  further  stage  of  heterophoria, 
and  not  a  true  squint  nor  a  paralysis.  The  case 
of  Mr.  S.  H.,  page  195,  is  a  typical  example. 
Hi  e   methods  0/    testing  the  muscular  balance 


HETEROPHORIA 


169 


of  the  eyes. — In  a  case  of  heterophoria,  under 
ordinary  circumstances,  the  desire  for  binocular 
vision  prevents  the  eyes  from  deviating  from 
their  normal  relative  directions.  But  if,  by 
artificial  means,  the  image  formed  in  one  eye 
be  so  altered  in  appearance  or  position  as  to 
make  fusion  with  the  other  unaltered  image  im- 
possible, the  control  of  the  fusion-sense  is  sus- 
pended. The  heterophoria  then  gives  rise  to  a 
manifest   deviation.      The   altered    image   in    the 


deviating  eye  is  not  suppressed  as  in  a  case  of 
squint.  The  diplopia,  therefore,  gives  an  easy 
means  of  ascertaining  the  direction  and  degree 
of  the  deviation.  This  is  the  principle  on  which 
all  subjective  tests  for  heterophoria  are  based. 

The  instruments  required  for  the  tests  which 
I  am  about  to  describe  are  the  Maddox  rod  and 
tangent  scale,  the  Maddox  double  prism,  an 
adjustable  trial  frame,  test  cards,  and  a  set  of 
prisms  whose  axes  are  accurately  marked.  A 
rotary  prism  also  is  very  useful. 


I  JO  HETEROPHORIA 

The  Maddox  rod  (fig.  1 9).  A  transparent  round 
glass  rod  is,  in  effect,  a  very  strong  cylindrical  lens. 
Rays  of  light,  therefore,  which  pass  through  it 
are  dispersed  in  one  plane  only,  at  right  angles  to 
the  axis  of  the  rod.  So  that  if  a  point  of  light  be 
looked  at  through  this  rod,  it  will  appear  as  a  long- 
narrow  band  of  light.  For  the  sake  of  convenience, 
half  a  dozen  of  these  pieces  of  glass  rod  are  fixed, 
side  by  side,  in  a  metal  disc  of  such  a  size  as  to 
fit  into  an  ordinary  trial  frame.  The  rods  are 
generally  made  of  red  glass,  to  increase  the  con- 
trast between  this  band  of  light  and  the  true 
image.  An  equally  good  plan  is  to  have  the 
rods  made  of  colourless  glass  and  to  put  a  plane 
red  glass  before  the  other  eye. 

In  looking  at  a  flame,  with  the  rod  before  one 
eye  and  the  other  eye  naked,  the  naked  eye  will  of 
course  see  the  flame  and  the  surrounding  objects  ; 
but,  to  the  rod-clad  eye,  the  flame  will  appear  as 
a  long  streak  of  light,  and  less  luminous  objects 
will  not  be  visible  at  all.  It  is  not  possible  to 
blend  two  such  dissimilar  images  as  the  Maine  and 
the  streak,1  so  the  function  of  fusion  is  temporarily 


1  The  images  should  be  differently  coloured.  The  rods 
should  be  carefully  fitted  side  by  side,  so  that  it  is  not 
possible  to  see  between  them.  The  source  of  light  at  the 
zero  of  the  scale  should,  if  possible,  be  a  frosted  incan- 
descent electric  lamp.  Failing  this,  any  bright  flame, 
enclosed  in  a  tin  chimney  having  a  hole  of  about  i£  inch 
diameter  in  one  side  of  it,  will  serve  the  purpose.  The 
room  should  not  be  too  brightly  illuminated.     As  the  rods 


HETEROPHORIA 


171 


suspended,  and  the  eyes  are  merely  controlled  by 
their  motor  coordinations.  If  there  be  no  motor 
anomaly,  the  streak,  seen  by  the  rod-clad  eye, 
will  appear  to  pass  through  the  flame,  seen  by  the 


<  .  - 

\ 
3 

J 

l a 1 1 2 2 


9-8-7-6-J-V3*i'1-i-l-a'3«V-l*6-7-8-SI-'o 


Fig.  20 


naked  eye.  But  if  there  be  any  heterophoria  it 
will  now  be  able  to  cause  the  eyes  to  deviate,  the 
relative  positions  of  the  streak  and  light  indicating 
the  direction  and  degree  of  the  deviation. 


produce  extreme  distortion  in  one  direction  only,  a  well 
marked  vertical  line  can  be  seen  through  the  rods  when 
their  axes  are  horizontal,  and  a  horizontal  line  can  be  seen 
when  their  axes  are  vertical.  Care  should  therefore  be 
taken  that  there  be  no  prominent  horizontal  or  vertical  lines 
near  the  centre  of  the  field  of  vision.  F'or  this  reason,  the 
paper  on  which  the  tangent  scale  is  printed  should  be  of 
nearly  the  same  colour  as  the  background  on  which  it  is 
hung :  or  the  large  figures  may  be  marked  on  the  wall 
itself.  With  these  precautions,  I  have  always  found  the 
rod  test  quite  reliable. 


172  HETEROPHORIA 

The  tangent  scale  is  shown  in  fig.  20.  The 
large  figures  on  the  horizontal  and  vertical  scales 
denote  tangents  to  degrees  at  a  distance  of  5 
metres.  A  small  electric  or  other  light  is  placed 
at  the  zero  of  the  scale. 


Fig.  21. 

The  Maddox  double  prism  (fig.  21)  consists  of 
two  prisms,  each  of  40,1  cemented  base  to  base. 
When  this  double  prism  is  placed  with  its  apices 
vertical,  before  one  eye,  so  that  the  line  of  junc- 
tion  of  the  bases  crosses  the  pupil  horizontally, 

1  To  avoid  confusion,  the  strength  of  a  prism  is  always, 
in  this  book,  denoted  by  the  number  of  degrees  which  it 
deflects  a  ray  of  light.  Chromatic  dispersion  produces  110 
appreciable  error  in  the  weak  prisms  used  in  ophthalmology. 

An  optician  usually  numbers  a  prism  according  to  the 
widtli  of  its  geometrical  angle  (the  angle  between  the  two 
plane  surfaces).  The  refracting  power  of  such  a  prism 
varies  according  to  the  kind  of  glass  of  which  it  is  made. 
For  practical  purposes  it  may  be  taken  as  half  the  geo- 
metrical angle.  For  instance,  a  prism  which  deflects  .1  raj 
of  light  to  the  extent  of  4  will  have  a  geometrical  angle 
of  about  8°. 


HETEROPHORIA  I J$ 

two  false  images  of  any  small  object  will  be  seen, 
one  above  and  the  other  below  its  true  position. 
If  now  the  other  (naked)  eye  be  opened,  it  will 
see  the  real  image  of  the  object  mid-way  between 
the  two  false  images.  The  false  images  are  not 
changed  in  appearance,  but  the  vertical  displace- 
ment of  each  is  too  great  to  admit  of  the  true 
imaoe  beino-  blended  with  either  of  them.  The 
eyes  are  thus  temporarily  deprived  of  the  control 
of  the  fusion  sense  and  abandoned  to  their  motor 
coordinations,  just  as  in  the  last  test. 

In  looking  at  a  horizontal  line,  the  true  image 
can  of  course  not  be  made  to  approach  either  of 
the  two  false  images  ;  but  care  must  be  taken  that 
there  be  no  long  vertical  line  near  the  centre  of 
the  field  of  vision. 

The  test  cards  which  I  use  consist  of  two  pieces 
of  strong  white  cardboard  each  2  feet  square. 
Number  I.  card  has  in  its  centre  a  straight  black 
line  2  inches  long.  In  the  centre  of  Number  II. 
card  are  ten  letters  of  "  Pearl  "  type  having  a 
large  capital  O  in  the  middle.  The  cards  are 
meant  for  use  at  the  reading  distance.  The 
reason  for  making  them  so  large  is  that  the 
objects  shall  be  seen  in  the  centre  of  a  blank 
field  with  no  edges  near  to  solicit  fusion. 

In  the  examination  I  begin  with  the  Maddox 
rod.  The  patient  is  seated  before  the  tangent 
scale,  at  a  distance  of  5  metres  from  it.  If  he  be 
not  absolutely   emmetropic,    he  wears  correcting 


1/4  IIKTEROPHORIA 


Number  I.  test  card. 
Fig.  22. 


Nu in lu-r  II.   test  card. 

Fig.  23. 


HETEROPHORIA  1 75 

lenses  in  the  trial  frame  in  every  test.  The  frame 
is  adjusted  so  that  the  lenses  are  accurately  centred 
for  distant  vision.  The  rod,  with  its  axis  horizon- 
tal, is  put  in  the  frame  before  the  right  eye.  The 
light,  at  the  zero  of  the  tangent  scale,  is  switched 
on.  If  the  vertical  streak,  seen  by  the  right  eye, 
appears  to  go  through  the  light,  seen  by  the  left 
eye,  the  patient  has  no  esophoria  or  exophoria  in 
distant  vision.      Now   rotate  the  rod   so  that   its 


Fig.  24.1 

axis  is  vertical.  If  the  horizontal  streak,  now  seen 
by  the  right  eye,  appears  to  pass  through  the  light 
seen  by  the  left  eye,  the  patient  has  no  hyper- 
phoria in  distant  vision. 

Now  remove  the  rod  and  replace  it  with  the 
double  prism,  with  apices  vertical  (line  of  junction 
of  bases  horizontal).  Adjust  the  trial  frame  for 
near  vision.  Let  the  patient  hold  in  his  hand 
Number    I.    test    card,    with    the  line  horizontal. 

1  This  and  the  two  succeeding  figures  are  taken  from 
a  paper  on  "  Insufficiency  of  the  Obliques,"  by  Dr.  Savage, 
of  Nashville,  U.S.A.,  "Archives  of  Ophthalmology,"  Janu- 
ary, 1S91.  "Ophthalmic  Myology,"  by  the  same  author, 
contains  the  fullest  account  of  cyclophoria  which  has 
hitherto  been  published. 


1  j6  IIETEROPHORIA 

He  will  see  two  false  images  of  the  horizontal 
line  with  the  prism-clad  eye,  and  between  them, 
he  will  see  the  true  image  with  the  naked  eye. 
If  the  middle  line  appears  equidistant  from  each 
of  the  other  lines,  and  has  its  ends  level  with  their 
ends  (fig.  24)  there  is  no  hyperphoria,  esophoria, 
or  exophoria  in  near  vision.  If  the  middle  line 
appears  parallel  to  the  other  two  lines,  as  in 
this  figure,  there  is  no  cyclophoria.  The  patient's 
oculo -motor  equilibrium,  therefore,  is  perfect  in 
every  respect. 

If,  however,  any  anomaly  be  found  during  these 
proceedings,  further  examinations  will  be  required. 

In  the  distant  vision  test  with  the  Maddox  rod, 
axis  horizontal,  before  the  right  eye,  if  the  vertical 
streak  lies  to  the  right  of  the  light  (homonymous 
diplopia),  there  is  esophoria.  If  it  lies  to  the 
left  of  the  light  (crossed  diplopia),  there  is  exo- 
phoria. The  figure  on  the  tangent  scale,  through 
which  the  vertical  streak  passes,  numerates  the 
degree  of  the  defect.  As  a  control  test,  change 
the  rod  from  the  right  eye  to  the  left.  The  posi- 
tion of  the  streak  also  changes  over,  that  is,  it 
still  shows  the  same  kind  of  diplopia.  The 
degree  of  heterophoria  indicated  is  the  same  as 
before.  Now  place  before  one  eye  a  prism  of 
the  same  degree  as  the  defect,  base  out  in  eso- 
phoria, base  in  in  exophoria.  This  should  cause 
the  streak  to  pass  through  the  light. 

In   using  the  rod,  axis  vertical,  before  the  right 


HETEROPHORIA  \JJ 

eye,  if  the  horizontal  streak  is  seen  below  the  light, 
this  indicates  that  the  right  eye  tends  to  turn 
upwards  relatively  to  the  left  eye  (right  hyper- 
phoria). If  the  streak  is  seen  above  the  light, 
the  left  eye  tends  to  turn  upwards  relatively  to 
the  right  eye  (left  hyperphoria).  The  figure,  on 
the  vertical  scale,  which  the  streak  appears  to 
cross,  numerates  the  degree  of  the  hyperphoria. 
Now  change  the  rod  from  the  right  to  the  left 
eye.  Almost  invariably,  if  the  right  eye  saw  the 
streak  above  the  light,  the  left  eye  will  now  see  it 
below,  and  vice  versa.  That  is  to  say,  the  hyper- 
phoria is  comitant.  The  result  should  be  checked 
by  neutralising  the  hyperphoria  with  a  prism  of 
the  strength  indicated  by  the  position  of  the 
streak. 

In  rather  rare  instances  it  happens  that  each 
eye,  in  turn,  rotates  upwards  behind  the  rod 
(double  hyperphoria). 

In  the  near  vision  test  with  the  double  prism 
before  the  right  eye,  and  the  Number  I.  test  card, 
the  middle  line,  seen  by  the  left  eye,  should  be 
equidistant  between  the  two  false  images,  seen  by 
the  right  eye.  If  it  lies  nearer  the  upper  false 
image,  there  is  right  hyperphoria.  If  it  lies 
nearer  the  lower  false  image,  there  is  left  hyper- 
phoria. The  prism,  base  down,  before  the  hyper- 
phoria eye,  which  places  the  line  half-way  between 
the  two  false  images,  will  serve  to  measure  the 
degree  of  the  anomalv. 


i  ;8 


IIKTEROPHORIA 


If  the  three  lines  are  not  all  level  with  each 
other  at  the  ends,  hand  the  patient  Number  II. 
test  card  and  tell  him  to  read  the  letters  on  it. 
The  small  letters  are  to  ensure  a  normal  effort 
of  accommodation.  If  presbyopic,  the  patient  is 
allowed  glasses.  He  will  see  the  true  image  of 
the  object  between  its  two  false  images.  In  ortho- 
phoria the  three  images  will  be  in  the  same 
vertical  line.  If  the  middle  image,  seen  by  the 
left  eye,  is  to  the  left  of  the  two  false  images,  the 


patient  has  esophoria  in  near  vision.  If  it  is  to 
the  right,  he  has  exophoria  in  near  vision.  The 
prism,  axis  horizontal,  which  will  bring  the  three 
O's  in  line,  is  a  measure  of  the  defect.  In  near 
vision  it  is  better  to  measure  with  prisms  than  to 
use  any  kind  of  small  tangent  scale,  because  with 
the  former  the  distance  from  the  eye  is  of  no 
consequence,  whereas  with  the  latter  the  smallest 


HETEROPHORIA  179 

variation  introduces  an  error.  The  study  of  eso- 
phoria  and  exophoria  in  near  vision  is  intimately 
associated  with  that  of  convergence  anomalies. 

When  the  patient  looks  at  the  horizontal  line 
on  Number  I.  card,  with  both  eyes  open  and  the 
double  prism  before  the  right  eye,  the  three  lines 
should  be  parallel  (fig.  24).  If  not,  there  is  cyclo- 
phoria.  Suppose  the  middle  line,  seen  by  the 
left  eye,  seems  to  dip  down  to  the  left  as  in  fig.  25, 
this  shows  that  the  vertical  meridians  of  the  eyes 
are  leaning  in  the  opposite  direction,  towards  each 
other  (minus  cyclophoria).  If  the  middle  line, 
seen  by  the  left  eye,  appears  to  dip  down  to  the 
right  as  in  fig  26,  there  is  plus  cyclophoria. 

Prism  duction  should  always  be  investigated  in 
any  case  in  which  heterophoria  has  been  found. 

Seat  the  patient  at  a  distance  of  five  or  six 
metres  from  a  candle  flame.  Let  him  wear  a  trial 
frame.  While  he  looks  steadily  at  the  light,  put 
a  i°  prism,  apex  up,  before  the  right  eye.  Grad- 
ually increase  the  strength  of  the  prism,  until  the 
highest  prism  is  found  which  the  patient  can  bear 
without  seeing  double.  This  indicates  the  extreme 
range  of  superduction  of  the  right  eye.  Now  test 
the  superduction  of  the  left  eye.  The  subduction 
of  each  eye  is  similarly  tested,  with  prisms  apex 
down.  The  power  of  binocular  abduction  is 
tested  with  prisms  apex  out.  Binocular  adduction 
is  so  intimately  associated  with  accommodation 
that  an  attempt  to  measure  it  with  prisms  (which 


I  So  HETEROPHORIA 

cause    the   eyes   to   converge    without   accommo- 
dating) gives  very  variable  and  misleading  results. 
The   normal    limits    of   prism    duction    are    as 
follows  : — - 

Superduction  ...  ...      i^-°  to  i\° 

Subduction      i|°  to  2J-0 

Abduction        ...  ...       40   to  50 

No  amount  of  practice  appears  to  increase  the 
duction  power  in  these  three  directions.  Con- 
vergence,  on   the  other  hand,  can  nearly  always 


Fig.  27. 

be  much  increased  by  practice.  As  the  degree 
of  prism-duction  does  not  vary  from  time  to  time, 
and  is  independent  of  voluntary  effort  on  the  part 
of  the  patient,  the  information  obtained  is  reliable. 
A  rotary  prism,  (fig.  27)  is  very  convenient  for 
measuring  duction.  It  consists  of  two  prisms  of 
equal  strength,  mounted  in  a  metal  disc  in  such  a 
position  that  the  apex  of  each  coincides  with  the 
base  of  the  other.  In  this  position  they,  of  course, 
neutralise  each  other.      By  a  mechanical  arrange- 


HETEROPHORIA 


181 


ment,  the  two  prisms  can  be  rotated  in  opposite 
directions  at  equal  rates.  The  strength  of  the 
compound  prism  can  be  thus  gradually  increased 
from  zero  up  to  the  combined  strength  of  the  two 
components. 


Fig.  zi 


Phorometer. — Fig.  28  shows  an  instrument  which  I 
have  found  very  useful  for  measuring  heterophoria.  A 
rod-shaped  wooden  box  24  inches  by  2  inches  by  2  inches, 
is  supported  on  a  stand  by  a  horizontal  bolt,  so  that  it 
is  free  to  rotate  in  a  vertical  plane.     (A  two-foot  length 

13 


1 82  HETEROPHORIA 

of  brass  optical  tube  would  do  as  well  as  the  rod- 
shaped  box).  In  the  face  of  this  rod-shaped  box  are 
three  openings,  each  3  inches  by  -§  inch.  In  the  centre 
opening  is  fitted  a  piece  of  frosted  red  glass.1  In  each 
of  the  two  other  openings  is  a  piece  of  frosted  green 
glass.  In  the  box,  behind  each  glass,  is  a  small  electric 
lamp  having  a  tin  reflector  behind  it  to  increase  the 
illumination.  The  box  is  ventilated  by  holes  in  the 
back.  On  the  back  of  the  stand  is  a  brass  protractor, 
marked  in  degrees,  to  show  the  axis  at  which  the  rod- 
shaped  box  is  placed. 

The  room  is  partially  darkened  by  drawing  down 
the  blinds.  The  patient  is  seated  in  front  of  the 
instrument  at  a  distance  of  about  8  or  10  feet.  In  a 
trial-frame  he  wears  a  red  glass  before  the  right  eye, 
and  a  green  glass  before  the  left.  With  the  right  eye 
he  sees  nothing  but  the  centre  red  light ;  and  with  the 
left  eye  he  sees  nothing  but  the  two  green  lights. 
The  angular  distance  between  the  lights  is  sufficiently  great 
to  avoid  any  tendency  to  fuse  the  red  light  with  cither  of 
the  green  lights,  so  that  the  eyes  are  perfectly  dissociated. 
First  the  rod-shaped  box  is  put  horizontal  and  the 
patient  is  asked  whether  the  three  lights  appear  in  the 
same  straight  line.  If  they  do,  he  has  no  hyperphoria. 
If  the  red  appears  below  the  level  of  the  green  lights, 
he  has  right  hyperphoria.  If  it  appears  above,  he  has 
left  hyperphoria.  The  degree  of  the  defect  is  measured 
by  putting  a  rotary  prism  (fig.  27)  in  the  trial-frame 
and  screwing  it  up  until  the  lights  appear  in  line. 
Esophoria  and  exophoria  are  similarly  detected  and 
measured  by  placing  the  rod-shaped  box  vertical — red 
to  the  right  indicating  esophoria,  and  red  to  the  left, 
exophoria. 

1  I  believe  that  Mr.  Lang  was  the  first  to  use  Snellen's 
coloured  glasses  for  the  measurement  of  heterophoria.  His 
apparatus  is  described  in  "  The  Methodical  Examination 
of  the  Eye,"  page  52. 


HETEROPHORIA  I»3 

If  one  wishes  to  ascertain  the  direction  of  a  com- 
pound defect,  such,  for  instance,  as  esophoria  with 
right  hyperphoria,  the  box  is  rotated  until  the  lights 
are  in  the  same  straight  line,  though  of  course  not 
equidistant  from  each  other.  The  axis  is  then  read  off 
from  the  protractor  at  the  back  of  the  stand.  To 
ascertain  the  degree  of  the  compound  defect,  place  the 
box  with  its  axis  at  right  angles  to  this,  then  screw  up 
the  rotary  prism  until  the  lights  are  again  in  the  same 
straight  line. 

Esophoria. 

The  liability  of  an  esophoria  to  cause  trouble  is 
determined  not  so  much  by  its  degree  as  by  the 
condition  of  the  functions  of  abversion  and  binocu 
lar  abduction.  A  patient  who  can  abvert  each 
eye  separately  until  the  cornea  touches  the  outer 
canthus,  and  whose  binocular  abduction  is  not 
less  than  30,  will  as  a  rule  be  able  to  support 
many  degrees  of  esophoria  without  inconvenience. 

In  many  cases  of  esophoria  of  high  degree 
there  is  occasional  momentary  diplopia.  When 
the  patient  is  gazing  vacantly  without  perceiving 
what  is  before  his  eyes,  perhaps  the  visual  axes 
may  deviate.  Instantly  the  diplopia  awakens  the 
dormant  fusion  sense,  and  the  eyes  immediately 
recover  themselves.  These  cases  are  often  mis- 
taken for  occasional  convergent  squint.  Occa- 
sional squints,  however,  differ  from  esophoria  in 
that  the  fusion  sense  is  defective,  so  that  the 
deviation  is  not  so  instantly  corrected,  and  diplopia 
is  either  absent  or  very  faint.      In  an  occasional 


184  HETEROPHORIA 

squint,  too,  examination  with  the  Maddox  rod 
shows  that  when  the  deviation  is  not  actually 
present  there  is  little  or  no  tendency  to  con- 
vergence. In  a  case  of  occasional  squint,  we 
have  a  pair  of  eyes,  not  properly  controlled  by 
the  fusion  sense,  responding-  to  intermittent  and 
varying  nervous  impulses.  In  esophoria  there  is 
a  constant  and  definite  motor  anomaly  which  is 
kept  in  check  by  a  perfect  fusion  faculty. 

Treatment. — Moderate  degrees  of  esophoria 
never  cause  inconvenience  unless  the  binocular 
abduction  is  very  deficient.  In  these  cases  the 
symptoms  are  relieved  by  the  constant  wearing 
of  prisms,  apex  in,  which  represent  the  deficiency 
of  binocular  abduction  [not  the  degree  of  eso- 
phoria). The  prism  should  be  divided  between 
the  two  eyes.  For  example,  a  patient  with  50  of 
esophoria  will  probably  not  be  inconvenienced 
thereby.  But  if  his  binocular  abduction  is  only 
20  instead  of  40  he  is  likely  to  suffer  from  "  asthe- 
nopic "  symptoms  and  occasional  diplopia.  He 
will  be  relieved  by  wearing  prisms,  apex  in, 
having  a  total  deviating  power  of  20.  If  the 
patient  already  wears  glasses  for  correction  of  a 
focal  error,  the  prismatic  effect  may  perhaps  be 
got  by  decentration  of  lenses  (see  Appendix). 

In  a  case  of  esophoria  of  high  degree  requiring 
treatment,  operation  is  the  only  resort.  If  the 
esophoria  is  not  less  then  70  in  distant  vision, 
and    the   near  vision   test  shows   the  same   or  a 


HETEROPHORIA  185 

higher  degree,  and  if  abversion  and  binocular 
abduction  are  not  markedly  below  normal,  the 
best  procedure  is  complete  central  tenotomy  of 
an  internal  rectus,  by  the  method  described  on 
p.  216.  If  the  degree  of  esophoria  is  less  in 
near  vision  than  in  distant  vision,  tenotomy  is 
contra-indicated.  In  a  case  of  esophoria  of  high 
degree,  with  abduction  less  than  2°,  and  abver- 
sion subnormal,  and  frequent  momentary  diplopia, 
advancement  of  an  external  rectus  should  be 
performed. 

Exophoria. 

Uncomplicated  exophoria  of  moderate  degree 
seldom  causes  any  inconvenience.  But  if,  as 
occasionally  happens,  there  is  a  defect  of  dynamic 
convergence  in  addition,  the  patient  is  likely  to 
suffer  from  frontal  headache,  not  only  after  using 
the  eyes  in  near  vision,  but  often  at  other  times 
also.  In  cases  of  exophoria  of  high  degree  the 
eyes  may  momentarily  deviate,  but  this  is  less 
common  than  in  esophoria. 

Treatment. — Prisms  are  seldom  of  use  in  exo- 
phoria. Slight  cases  require  no  treatment,  if 
uncomplicated.  If  the  case  be  complicated  by 
convergence  deficiency,  treatment  should  be 
directed  to  this  anomaly.  Even  if  there  be  no 
deficiency  of  dynamic  convergence,  convergence 
training  often  relieves  the  patient's  symptoms, 
but,  in  my  experience,   the  effect  has  been  only 


jS6  heterophoria 

transitory.  In  higher  degrees  of  exophoria,  espe- 
cially if  adversion  be  deficient,  the  internal  rectus 
muscle  should  be  advanced.  One  should  then 
aim  at  producing  an  operative  effect  exactly  equal 
to  the  degree  of  the  exophoria  of  distant  vision, 
Exophoria  is  almost  invariably  due  to  under- 
action of  the  internal  recti,  scarcely  ever  to  over- 
action  of  the  externi.  For  this  reason,  tenotomy 
of  the  rectus  externus  is  not  advisable. 

Hyperphoria. 

Clinically,  hyperphoria  is  the  most  important  of 
all  forms  of  heterophoria,  because  of  the  severity 
of  the  symptoms  to  which  it  is  liable  to  give  rise, 
and  the  certainty  with  which  these  symptoms  may 
be  relieved.  The  liability  of  a  case  to  cause 
trouble  depends  not  only  upon  the  degree  of  the 
hyperphoria,  but  upon  the  extent  of  any  deficiency 
of  prism-duction  in  the  opposite  direction.  For 
instance,  an  ordinary  healthy  man  who  has  |°  of 
rio-ht  hyperphoria  will  probably  suffer  no  incon- 
venience if  the  right  subduction  is  as  much  as  2°: 
but  if  it  is  only  i°  or  less,  he  is  almost  certain  to 
have  trouble. 

The  commonest  symptom  is  frontal  headache, 
coming  on  towards  the  end  of  the  day,  not  espe- 
cially caused  by  near  work.  Some  patients  com- 
plain of  giddiness  on  looking  down.  Momentary 
diplopia  is  not  uncommon. 

In  a  marked  case  of  hyperphoria,   more  often 


HETEROPHORIA  1 87 

than  not,  the  palpebral  fissure  on  the  hyper- 
phoria side  is  smaller  than  that  on  the  other. 
This  asymmetry  disappears  entirely  when  the 
hyperphoria  is  corrected. 

The  treatment,  in  any  case  of  hyperphoria  of 
moderate  degree,  is  by  prisms  to  be  worn  con- 
stantly. The  prism  should  be  placed,  apex  up, 
before  the  hyperphoric  eye.  Or,  if  more  than  i° 
is  required,  the  effect  may  be  divided  between  the 
two  eyes,  the  prism  before  the  other  eye  being 
placed,  of  course,  apex  down.  The  strength  of 
the  prisms  should  be  determined  partly  by  the 
degree  of  the  hyperphoria  and  partly  by  the 
range  of  prism  duction  (see  page  179).  One 
should  attempt  as  nearly  as  possible  to  correct 
the  hyperphoria  and  to  bring  each  eye  into  the 
middle  of  the  vertical  range  of  prism  duction. 
For  example,  take  a  case  of  right  hyperphoria  20, 
in  which  the  right  superduction  (and  left  subduc- 
tion)  is  30  and  the  right  subduction  (and  left 
superduction)  is  i°.  A  prism,  apex  up,  before 
the  right  eye,  20  would  correct  the  hyperphoria  : 
but  a  prism  of  i°  would  suffice  to  bring  the  eye 
into  the  middle  of  the  range  of  prism  duction. 
In  this  case  one  would  order  a  prism  of  il-0  as  a 
compromise. 

If  the  hyperphoria  is  very  high — over  40 — 
operation  is  usually  indicated.  If  subduction  of 
the  hyperphoric  eye  is  not  less  than  i°,  and  super- 
duction over  40,  complete  central  tenotomy  of  the 


1 88  HETEROPHORIA 

superior  rectus  of  this  eye  is  the  best  procedure. 
In  a  case  of  hyperphoria  of  very  high  degree, 
with  very  deficient  subduction,  the  inferior 
rectus  muscle  of  the  hyperphoric  eye  should  be 
advanced. 

I  have  seen  a  few  well-marked  cases  of  so-called 
double  hyperphoria.  In  all  there  was  more  or  less 
drooping  of  both  eyelids.  A  great  effort  was 
required  to  open  the  eyes  widely  while  looking 
straight  ahead,  but  in  looking  up,  the  lids  were 
lifted  normally.  Either  eye  turned  up  when 
screened.  Subduction  of  either  eye  was  normal. 
These  cases  were  possibly  due  to  a  faulty  nervous 
connection  between  the  superior  recti  muscles  and 
the  levatores  palpebral  superiores.  In  two  of  these 
cases  I  performed  complete  central  tenotomy  of 
both  superior  recti,  with  excellent  results. 

I  have  seen  several  cases  of  double  hyper- 
phoria associated  with  plus  cyclophoria  —  due 
probably  to  underaction  of  the  superior  oblique 
muscles. 

I  have  no  note  of  any  case  of  double  kata- 
phoria  (downward  tendency  of  each  eye). 

Cyc/ophoria. 

In  order  that  binocular  vision  may  be  possible 
it  is  necessary  not  only  that  the  visual  axes  of  the 
two  eyes  shall  be  directed  to  the  same  object,  but 
that  their  vertical  diameters  shall  be  parallel. 
The    work     of     keeping    the    vertical     diameters 


HETEROPHORIA  1 89 

parallel  falls  almost  entirely  upon  the  oblique 
muscles.  If  the  superior  obliques  act  too  feebly, 
the  eyes  tend  to  rotate  round  a  fore-and-aft  axis 
so  that  their  vertical  diameters  diverge  above 
(plus  cyclophoria.)  This  is  very  much  more 
common  than  minus  cyclophoria.  Plus  cyclo- 
phoria is  not  infrequently  associated  with  double 
hyperphoria. 

Cyclophoria  may  cause  nausea,  vertigo,  and 
difficulty  in  judging  the  true  position  of  the  steps 
in  going  downstairs. 

Not  much  can  be  done  in  the  way  of  direct 
treatment  in  cases  of  cyclophoria.  But  there 
are  some  practical  points  which  deserve  careful 
study. 

Close  one  eye,  and  hold  before  the  other  a 
strong  convex  cylindrical  lens,  axis  vertical.  Look 
at  a  horizontal  line,  the  junction  of  a  floor  and 
ceiling,  for  instance.  The  horizontal  line  still 
appears  horizontal.  Now  rotate  the  lens  a  few 
degrees.  The  horizontal  line  appears  to  rotate 
slightly  with  the  lens.  In  other  words,  the  cylin- 
drical lens  rotates  the  image  of  the  line  towards 
its  meridian  of  greatest  convexity. 

Next  put  on  a  trial-frame  and  place  before 
each  eye  a  +  i  d.  cylindrical  lens,  axis  vertical. 
Vision  will  be  slightly  blurred,  but  objects  will  not 
appear  displaced,  and  the  lenses  can  be  worn  for 
a  long  time  without  discomfort.  Now  rotate  each 
lens  about  300,  so  that  their  axes  diverge  above. 


190 


HETEROPHORIA 


On  looking  down,  the  floor  seems  far  away,  and, 
on  looking  up,  the  ceiling  seems  quite  near — one 
feels  about  7  feet  high.  Now  rotate  the  cylinders 
in  the  opposite  direction,  so  that  their  axes  con- 
verge above.  The  floor  appears  quite  near,  and 
the  ceiling  high — one  feels  a  dwarf.  After  a  few 
minutes  of  this  artificial  oblique  astigmatism,  one 
experiences  a  feeling  of  giddiness  and  nausea, 
reminiscent  of  the  "giant  stride"  in  one's  early 
school  days. 

In    the    light    of    the   former    experiment,   the 
explanation    is   plain.        We    are    accustomed    to 
localise  all  objects  with  reference  to  the  horizontal 
surface  (floor,  ground,  or  sea)  which  supports  us. 
While  wearing  the   convex   cylinders  with    axes 
divergent    above,    the   images    of    the   horizontal 
surface   of  the   floor  are  tilted  outwards  towards 
each  temple.      In  order  that  these  images  may  be 
received   upon   corresponding   points  of   the  two 
retinae,  each  eye  must  rotate  about  a  fore-and-aft 
axis  so  that  the  vertical  diameters  diverge  above. 
This  is  accomplished  by  a  lessened  action  of  the 
superior  oblique  muscles  and  an  increased  action 
of  the   inferior  obliques.      But  this  has  also   the 
effect  of  rotating  the  two  eyes  a  little  upwards. 
So  that,  in  looking  down  to  the  floor,  one  has  to 
put  forth  sufficient  energy  to  overcome  this  up- 
ward   tendency,  as   well    as    to    effect   the   actual 
downward     rotation.        And    in    looking    at    the 
ceiling,  less  than  the  normal  expenditure  of  energy 


HETEROPHORIA  I  9  I 

is  required,  owing  to  the  eyes  already  having  an 
upward  tendency.  We  depend  chiefiy  upon  the 
"  muscular  sense  "  of  the  external  ocular  muscles 
in  judging  the  relative  positions  of  objects. 
Therefore,  the  increased  effort  required  in  look- 
ing down,  makes  the  floor  appear  farther  away, 
and  the  lessened  effort  in  looking  up,  makes  the 
ceiling  appear  lower. 

In  the  experiment  with  the  axes  of  the  cylinders 
convergent  above,  the  conditions  are  exactly 
reversed. 

This  experiment  appears  to  explain  the  com- 
monly observed  fact  that  astigmatism  is  more 
liable  to  cause  trouble  when  the  axes  are  oblique 
than  when  they  are  vertical  or  horizontal.  Un- 
corrected astigmatism,  unless  the  axes  in  the  two 
eyes  are  parallel  or  at  right  angles,  must  cause  a 
pseudo-cyclophoria,  which  should  disappear  when 
the  astigmatism  is  corrected. 

Now  and  then  one  meets  with  a  patient,  with 
oblique  astigmatism  who  is  less  comfortable  with 
glasses  which  accurately  correct  his  refractive 
error  than  he  was  without  any  correction  at  all. 
In  such  a  case,  one  generally  finds  that  he  has 
cyclophoria  of  an  opposite  kind  to  the  pseudo- 
cyclophoria  which  would  be  produced  by  his  un- 
corrected astigmatism.  So  that  they,  to  a  certain 
extent,  neutralised  each  other.  But,  with  the 
correction  of  his  astigmatism,  the  whole  of  his 
true    cyclophoria    becomes    manifest.        A    slight 


192 


HKTEROPIIORIA 


rotation,  say  about  50,  of  both  his  cylinders,  in  the 
direction  which  favours  the  feebly-acting  pair  of 
oblique  muscles,  will  often  make  him  quite  com- 
fortable without  appreciably  lowering  his  visual 
acuity. 

Under  certain  conditions  it  is  possible,  without  any 
rotation  of  the  eyes  round  a  fore  and  aft  axis,  to  blend 
images  of  lines  whicli  are  slightly  tilted  in  opposite 
directions  (see  page  11).  Some  authors  have  therefore 
assumed  that  the  eyes  never  make  an  axial  rotation  in 
the  interests  of  binocular  vision.  This  view  does  not 
accord  with  clinical  and  experimental  evidence.  Fu- 
sion of  tilted  images  takes  place  according  to  the  law 
stated  on  page  1 1 . 

Rhythmic  exercises  with  prisms,  cylinders,  &c, 
are  employed  by  many  eminent  ophthalmologists 
in  America.  1  have  thoroughly  tried  all  the  most 
approved  methods,  but  have  never  been  able 
to  satisfy  myself  that  I  have  produced  any  effect 
in  any  case  of  esophoria  or  hyperphoria.  Cases 
of  exophoria  are  indirectly  benefited  by  exer- 
cising the  dynamic  convergence,  but  that  is  a 
different  matter. 

In  America  there  is,  no  doubt,  a  tendency  to 
overestimate  the  importance  of  small  latent  devia- 
tion tendencies.  But  this  is  less  harmful  than 
the  almost  total  neglect  which  the  subject  meets 
with  in  this  country. 

Here  are  some  examples  : — 

Mr.  R.  H.t  aged  38,  a  hard  worker,  and  head  of  <i 
large  city  business,  consulted  me  on  October  17,  1899. 


HETEROPHORIA 


93 


He  complained  of  dull,  aching  pains  in  the  eyes  and 
forehead.  Pain  was  always  relieved  by  sleep.  It  was 
not  especially  associated  with  near  work.  He  suffered 
almost  as  much  during  his  holidays.  His  eyes  had 
been  examined  many  times,  and  he  had  worn  glasses 
for  twelve  years.  There  was  a  slight  drooping  of  the 
left  upper  lid.  He  was  wearing  +  2-25  D.  sph.  each 
eye.  He  showed  me  several  prescriptions  for  glasses, 
all  practically  the  same.  Retinoscopy  without  my- 
driatic showed  2  D.  of  hypermetropia  each  eye,  no 
astigmatism.  His  corrected  vision  was  £  easily,  each 
eye.  On  investigating  the  motor  balance  of  his  eyes, 
I  found  he  had  nearly  20  left  hyperphoria.  Left 
superduction  and  right  subduction  were  each  40  ;  and 
left  subduction  and  right  superduction  were  each  i°. 
I  ordered  spectacles  +  2  D.  sph.  each  eye,  the  right 
lens  to  be  combined  with  a  f°  prism,  apex  down,  and 
the  left  lens  with  a  similar  prism,  apex  up. 

On  September  26,  1902,  three  years  later,  I  saw  the 
patient  again.  He  has  worn  the  glasses  constantly, 
with  perfect  comfort,  and  is  entirely  free  from  the  old 
trouble. 

Miss  E.  B.,  aged  33,  seen  with  Mr.  Devereux  Mar- 
shall on  February  6,  1903.  Patient  had  suffered  from 
frontal  headache  and  occasional  diplopia  for  as  long  as 
she  could  remember.  Headaches  were  always  relieved 
by  sleep,  were  independent  of  occupation,  and  became 
more  severe  towards  the  end  of  the  day.  She  had  for 
many  years  worn  an  exact  correction  of  her  ametropia 
(4-  075  D.  cyl.  ax.  vert,  each  eye),  but  the  glasses  gave 
her  no  relief. 

On  investigating  the  motor  balance  of  the  eyes  we 
found  left  hyperphoria  40,  exophoria  i°.  Right  super- 
duction and  left  subduction  barely  i°.  Right  sub- 
duction and  left  superduction  each  6°.  We  ordered,  for 
constant  wear,  to  be  incorporated  with  her  cylinders, 
R.  E.  prisms  i^-°,  apex  down,  L.  E.  prism  i^°,  apex  up. 


194 


HETEROPHORIA 


The  patient  has  been  seen  twice  since  that  date. 
She  is  perfectly  comfortable  and  entirely  free  from 
headaches. 

Miss  F.  L.,  aged  17,  was  brought  to  me  on  February  2, 
1900.  She  was  wearing  spectacles  +  1  D.  sph.  She 
said  that  when  she  was  tired  her  eyes  would  often  be 
crossed  for  a  moment  and  she  then  would  see  double. 
The  crossing  of  the  eyes  only  lasted  an  instant.  She 
had  frequent  frontal  headaches.  She  had  worn  glasses 
since  she  was  ten  years  of  age.  She  had  been  told  that 
she  suffered  from  "  periodic  strabismus."  Retinoscopy 
without  mydriatic  showed  hypermetropia  of  0-5  D. 
only.  Vision  of  each  eye  f.  Examination  with  the 
Maddox  rod  and  tangent  scale  showed  esophoria,  90, 
in  distant  vision.  Esophoria,  in  near  vision,  was  8°. 
Binocular  prism  abduction  was  only  20.  R.  E.  could 
be  abverted  until  the  cornea  touched  the  outer  canthus. 
L.  E.  abversion  not  quite  so  complete.  The  fusion 
faculty  was  perfect.  The  case  was  not  one  of  "  periodic 
strabismus"  at  all,  but  an  example  of  esophoria  of 
high  degree. 

February  5,  1900. — Retinoscopy  was  confirmed  under 
atropine. 

February  20,  1900. —  I  advanced  the  left  external 
rectus  muscle  (of  course  without  tenotomising  the 
internus). 

February  27,  1900. — Stitches  removed. 

March  29,  1900. — Patient  has  t°  esophoria  in  distant 
vision,  perfect  orthophoria  in  near  vision,  binocular 
prism  abduction  50.  Patient  never  has  diplopia 
now. 

June  18,  1902. — Patient  has  not  been  seen  to  cross 
her  eyes  since  the  operation,  and  she  has  had  no 
diplopia.  She  is  quite  free  from  headaches  now.  She 
has,  of  course,  not  worn  glasses  since  the  operation. 

Captain  P.,  aged  about  30,  consulted  me  on  July  11, 
1899.     He  had  always  suffered  a  good  deal  from  head- 


HETEROPHORIA 


195 


aches,  and  had  had  occasional  momentary  diplopia, 
but  had  never  been  told  that  he  squinted.  Both  the 
headaches  and  the  diplopia  had  been  more  frequent 
since  he  had  "fever"  in  India  four  years  previously. 
He  had  had  his  eyes  examined  several  times,  and 
had  once  been  ordered  reading  glasses,  but  they  had 
done  no  good. 

Retinoscopy  showed  that  he  had  no  notable  refrac- 
tive error.  On  examining  the  motor  balance  of  his 
eyes,  he  was  found  to  have  left  hyperphoria  2^°.  His 
right  superduction  and  left  superduction  were  each 
scarcely  i°.  His  right  subduction  and  left  superduc- 
tion were  each  50.  Excursions  of  each  eye  separately 
were  quite  full. 

August  3,  1899. — On  repeating  the  examination,  I 
got  precisely  the  same  results.  As  there  was  no  refrac- 
tive error  which  would  necessitate  glasses,  I  did  not 
wish  to  burden  him  with  prisms,  I  therefore  advised 
operation. 

August  14,  1899. — I  performed  complete  central 
tenotomy  of  the  left  superior  rectus,  after  the  method 
described  on  page  216.  The  after  treatment  consisted 
only  of  a  shell  and  a  pad  of  gauze  worn  over  the  L.  E. 
for  a  few  days,  and  bathing  with  boric  lotion. 

August  29,  1899. — Wound  healed  and  eyes  perfectly 
comfortable.  There  is  now  right  hyperphoria  of  less 
than  i°. 

July  11,  1902. — Patient  has  been  free  from  head- 
aches and  the  occasional  diplopia  since  the  operation. 
There  is  now  no  measureable  degree  of  heterophoria. 
The  streak  of  light  with  the  rod  before  the  R.  E.  is 
at  the  upper  part  of  the  flame,  showing  left  hyperphoria 
of  less  than  £°. 

Mr.  S.  H. — I  saw  quite  recently  an  exceedingly 
instructive  case,  a  gentleman  aged  20,  sent  me  by  Dr. 
Bolton  Tomson.  From  early  childhood  until  one 
year  ago,  the  patient  had  suffered  from  severe  head- 


196 


HETEROPHORIA 


aches  coming  on  towards  the  end  of  the  day.  He  had 
occasional  diplopia,  one  image  being  over  the  other. 
He  also  had  frequent  attacks  of  typical  migraine. 
During  the  last  year,  he  has  seen  double  constantly, 
and  the  right  eye  has  squinted  downwards.  He  can 
still,  by  a  great  effort,  overcome  the  deviation  and 
blend  the  images.  The  diplopia  is  so  intense  that  he 
is  only  comfortable  when  one  or  other  eye  is  covered. 
But  since  the  hyperphoria  gave  place  to  an  actual 
deviation,  the  headaches  and  migraine  have  completely 
disappeared. 

There  is  no  important  refractive  error.  R.  E.  deviates 
downwards  (or  L.  E.  upwards)  8°.  Either  eye  deviates 
outwards  50.  Prisms  of  this  strength  give  binocular 
vision  with  orthophoria. 

I  propose  to  advance  the  L.  inferior  rectus  muscle, 
which  I  have  no  doubt  will  result  in  cure  of  the  whole 
trouble.  If  this  operation  had  been  performed  many 
years  ago  the  patient  would  have  been  spared  much 
unnecessary  suffering. 

Insufficiency  of  Dynamic  Convergence. 

This  is  not  a  heterophoria,  but  it  is  convenient 
to  discuss  it  in  this  chapter. 

There  has  been  much  confusion  on  the  subject 
of  insufficiency  of  convergence,  because  authors 
have  not  clearly  distinguished  between  static  and 
dynamic  convergence. 

A  person  whose  visual  apparatus  is  normal  has 
no  static  convergence  at  any  time  ;  in  distant 
vision  he  exercises  no  dynamic  convergence  ;  in 
near  vision  his  dynamic  convergence  exactly 
suffices  to  cause  both  visual  axes  to  be  directed 
to  the  near  object.      If  his  dynamic  convergence 


INSUFFICIENCY   OF   DYNAMIC   CONVERGENCE       197 

were  excessive,'  there  would  be  a  tendency  to  con- 
vergent squint  in  near  vision  ;  if  it  were  insuf- 
ficient, he  would  have  difficulty  in  maintaining 
convergence,  as  in  reading,  for  instance,  for  any 
length  of  time. 

A  person  who  has  a  convergent  squint,  which 
persists  after  correction  of  any  refractive  error, 
has  an  unchecked  static  convergence  ;  one  who 
has  esophoria  has  a  static  convergence  which  is 
kept  in  check  by  constant  muscular  effort,1  evoked 
by  the  desire  for  binocular  vision.  Static  con- 
vergence is  a  minus  quantity  in  divergent  squint. 
In  exophoria  there  is  a  minus  static  convergence 
which  is  neutralised  by  an  abnormal  effort  of 
dynamic  convergence.  In  these  cases  the  power 
of  dynamic  convergence  may  or  may  not  be 
normal. 

A  patient,  therefore,  who  has  exophoria  in 
distant  vision  and  the  same  degree  of  exophoria, 
or  less,  in  near  vision,  cannot  properly  be  said  to 
have  insufficiency  of  convergence.  This  dis- 
tinction between  exophoria  and  insufficiency  of 
dynamic  convergence  is  of  supreme  practical 
importance,  because  the  treatment  of  the  two 
affections  differs  entirely.  In  the  former  case,  if 
any  treatment  be  required  at  all,  operation  is 
usually   necessary  ;  in   the  latter,  operation  is  al- 

1  This  "  without  prejudice  "  to  the  much-debated  question 
of  the  existence  of  a  cerebral  centre  for  divergence. 

H 


198      INSUFFICIENCY    OF   DYNAMIC  CON  VERGE  NCE 

ways  contra-indicated,  and  benefit  may  often  be 
obtained  from  exercises. 

Insufficiency  of  dynamic  convergence,  apart 
from  neuropathic  cases,  is  not  common. 

The  symptoms  produced  by  insufficiency  of 
convergence  are  pain  in  the  brow  after  reading, 
and  a  tendency  to  hold  the  book  at  a  long  dis- 
tance from  the  eyes  (apart  from  any  error  of 
static  or  dynamic  refraction). 

Convergence  being  a  voluntary  act,  the  extreme 
degree  of  which  any  individual  is  capable  will 
vary  from  time  to  time,  according-  to  the  state  of 
his  health  and  the  amount  of  energy  he  is  able  to 
put  forth  at  the  moment.  Elaborate  instruments 
for  determining  the  near  point  of  convergence 
are,  therefore,  not  required.  Moreover,  this 
information  is  not  of  much  practical  use. 

The  best  procedure  is  to  test  the  horizontal 
motor  balance  of  the  eyes,  first  in  distant  vision. 
and  then  at  ten  inches.  If  there  is  no  more 
exophoria,  or  no  less  esophoria,  in  near  vision 
than  there  is  in  distant  vision,  the  patient  has  no 
insufficiency  of  convergence.  If  the  patient  has 
orthophoria  in  distant  vision  and  exophoria  in 
near  vision,  or  if  there  is  more  exophoria,  or  less 
esophoria,  in  near  than  in  distant  vision,  he  has 
insufficiency  of  dynamic  convergence  of  a  degree 
equal  to  the  difference. 

In  an  uncomplicated  case  of  insufficiency  oi 
convergence,    exercises    should    be    tried.         The 


INSUFFICIENCY  OF  DYNAMIC  CONVERGENCE     199 

following  procedure  is  as  good  as  any  : — Any 
error  of  static  or  dynamic  refraction  is  corrected 
by  glasses.  The  patient  begins  reading  a  book 
at  the  ordinary  distance.  Then,  while  still  read- 
ing, he  gradually  brings  the  book  nearer  his  eyes 
until  the  print  begins  to  be  blurred.  He  then 
slowly  removes  the  book  to  the  ordinary  reading 
distance.  This  is  repeated.  At  about  every 
tenth  line  he  looks  into  the  distance  for  a  moment, 
in  order  to  completely  relax  his  convergence. 
Two  or  three  pages  should  be  read  in  this  way, 
three  or  four  times  a  day  for  a  month.  This 
simple  plan  has  given  quite  as  good  results  as  the 
more  elaborate  methods  which  I  have  tried.  This 
is  perhaps  because  the  patient  finds  it  more  con- 
venient to  carry  out,  no  special  apparatus  being 
required. 

It  has  been  objected  that  the  accommodation  is  exer- 
cised at  the  same  time  as  the  convergence.  I  do  not 
think  that  it  would  be  advisable,  in  young  subjects  at  any 
rate,  entirely  to  dissociate  dynamic  convergence  from 
the  effort  of  accommodation  with  which  it  is  normally 
always  associated.  But  if  it  should  seem  advisable  to 
relieve  the  strain  on  the  accommodation  during  the 
exercises,  this  may  be  done  in  either  of  two  ways — the 
patient  may  wear  convex  glasses  so  as  to  exercise  less 
accommodation  with  a  given  amount  of  convergence, 
or,  what  comes  to  the  same  thing,  he  may  wear  prisms, 
apex  in,  so  as  to  exercise  more  convergence  with  a  given 
amount  of  accommodation. 

These  rhythmic  exercises  do  not  increase  the 
power  of  the  ocular  muscles  (any  more  than  voice 


200      INSUFFICIENCY   OF   DYNAMIC   CONVERGENCE 

training  increases  the  power  of  the  laryngeal 
muscles),  so  they  do  not  in  the  least  diminish 
exophoria  in  distant  vision.  But  they  often  much 
improve  the  power  of  dynamic  convergence,  by 
teaching  the  nervous  apparatus  to  respond  more 
readily  to  the  will. 

In  a  case  in  which  exercises  have  failed  and 
the  symptoms  are  troublesome  one  may,  as  a 
pis  aller,  order  prisms,  apices  out,  for  near  vision. 


201 


CHAPTER   XII. 

OPERATIONS   ON   THE   EXTERNAL   OCULAR 
MUSCLES. 

The  operations  commonly  performed  on  the 
muscles  of  the  eye  are  advancement  and  tenotomy. 
Either  of  these  measures  may  be  employed  alone, 
or  advancement  of  one  muscle  may  be  combined 
with  tenotomy  of  its  opponent. 

The  indications  for  these  operations  are  fully 
discussed  in  previous  chapters. 

Advancement. 

Very  many  different  methods  of  advancement 
of  a  rectus  muscle  have  been  described.  I  have 
tried  many  of  these  repeatedly,  also  two  methods 
of  shortening  the  tendon  by  folding  it  upon  itself. 
None  of  these  has  proved  entirely  satisfactory. 
With  practice,  one  can  always  make  sure  of 
inserting  the  sutures  firmly  in  the  tough  fibrous 
tissue  near  the  margin  of  the  cornea,  without 
putting  in  the  needle  dangerously  deeply.  The 
difficulty  is  with  the  end  of  the  sutures  attached 
to  the  muscle.  I  found  that  two  of  these  methods 
of  operating  gave  better  results  than  the  others. 
In  one  operation,  three  or  four  sutures  are  simply 


202  OPERATIONS 

passed  through  the  tough  circumcorueal  tissue, 
and  through  the  muscle,  and  tied.  If  these 
sutures  hold  for  a  week,  the  results  are  permanent. 
But  the  muscle  end  of  the  suture  often  cuts  its 
way  through  in  three  or  four  days.  And  in  any 
case,  one  has  to  produce  an  over  effect  at  the  time 
of  the  operation,  to  allow  for  slacking  of  these 
sutures,  so  that  precision  is  not  attainable  by  this 
method.  In  the  other  operation,  the  sutures  are 
knotted  on  the  muscle,  either  in  one  or  two  parts. 
This  nearly  always  gives  good  immediate  results, 
but  a  very  large  proportion  of  the  cases  relapse 
within  a  few  weeks.  This  is  probably  due  to  the 
fact  that  the  muscle  atrophies  in  front  of  the 
ligatures,  and  so  is  only  attached  to  the  globe 
by  its  lateral  expansions,  which  subsequently 
stretch. 

I  devised  the  following  operation  with  the 
object  of  combining  the  advantages  and  avoiding 
the  disadvantages  of  the  two  methods  to  which  I 
have  just  referred. 

The  Author s  Advancement  Operation. 
In  this  operation  a  firm,  unyielding  hold  is  got 
for  the  sutures  at  each  end,  so  that  any  desired 
degree  of  rotation  of  the  eyeball  may  be  produced. 
For  moderate  deviations,  I  advance  a  muscle 
without  tenotomising  its  opponent.  F"or  squints 
of  very  high  degree,  I  usually  first  tenotomise 
the   opposing   muscle  to  avoid  refraction  of   the 


OPERATIONS 


Fig.  29. 


?.; 


!04 

dobe. 


OPERATIONS 


The  anatomical  relations  of  the  advanced 
muscle  are  disturbed  as  little  as  possible.  As 
the   middle    part  of   the  muscle   is    not    included 


Fig.  34. 


in  the  sutures,  its  main  blood  supply  is  not 
interfered  with.  The  immediate  effect  produced 
is  the  final  result. 


OPERATIONS  205 

Instruments. — The  ordinary  advancement  in- 
struments are  required  :  Speculum  (fig.  29), 
straight  blunt-pointed  scissors  (fig,  34),  fixation 
forceps  with  projecting  teeth  which  take  a  firm 
hold  of  the  sclerotic  (fig.  36),  Prince's  advance- 
ment forceps,  right  and  left  (figs.  30  and  31),  or 
the  smooth  probe-pointed  forceps  (fig.  32),  needle 
holder  (fig.  t,^),  needles,  and  thread  ;  and  if  a 
tenotomy  is  to  be  done  at  the  same  time,  a 
tenotomy  hook  also  (fig.  35).  The  needles  I  use 
are  made  for  me  by  Messrs.  Weiss  and  Son. 
They  are  small,  curved  needles  with  large  eyes. 
They  must  be  very  sharp.  The  jaws  of  the 
needle  holder  which  I  use  (fig.  ^t,),  are  curved 
transversely  to  fit  these  needles.  Flat  jaws,  how- 
ever small,  are  apt  to  break  a  curved  needle. 
The  advancement  forceps  shown  in  fig.  32,  being 
smooth  and  probe-pointed,  is  easier  to  introduce 
than  the  ordinary  form  of  Prince's.  Both  blades 
being  alike,  only  one  forceps  is  required  instead 
of  two.  The  spring  is  strong  so  that  the  smooth 
blades  show  no  tendency  to  slip  under  any  strain 
to  which  one  ought  to  subject  the  tissues. 

The  blunt  instruments  are  sterilised  by  boiling 
for  five  or  ten  minutes  in  water  containing  a  little 
washing  soda.  The  scissors  are  boiled  for  about 
a  minute.  The  eyes  of  new  needles  are  cleared 
with  the  point  of  a  sewing  needle.  The  needles 
are  then  boiled  for  not  more  than  a  minute,  before 
being  threaded.      1  used  to  use  only  new  needles, 


206  OPERATIONS 

to  ensure  their  being  as  sharp  as  possible.  I  find, 
however,  that  it  is  quite  easy  to  sharpen  them  on 
a  fine  oiled  stone  ;  even  new  needles  can  be  much 
improved.  They  should  then  be  kept  in  a  flannel 
book  ;  the  paper  in  which  they  arc  sold  is  apt  to 
injure  delicate  points. 

The  suture  material  is  a  very  important  detail. 
It  should  be  thick.  The  thin  stuff  sold  as  "  eye 
silk"  cuts  like  a  knife.  I  use  thick  black  silk 
prepared  as  follows  :  A  reel  of  the  silk  is  wound 
loosely  round  a  winder  (made  by  bending  up  a 
piece  of  wire).  It  is  boiled  in  water,  to  sterilise 
it  and  to  remove  the  superfluous  colouring 
matter.  It  is  then  dried  before  a  fire.  The  end 
of  the  silk  is  then  threaded  through  a  large  glass 
bead.  The  glass  bead  is  then  dropped  into  a 
glass  beaker  containing  a  very  hot  mixture  of 
white  beeswax,  three  parts,  and  white  vaseline, 
five  parts.  The  whole  of  the  silk  is  drawn 
through  the  boiling  mixture,  and  is  wound  on 
a  large  glass  reel.  It  is  kept  in  a  sterilised 
glass  jar,  always  ready  for  use  without  further 
preparation. 

In  preparing  for  the  operation,  a  piece  of  the 
silk,  about  a  foot  long,  is  drawn  out  of  the  jar  with 
sterilised  forceps  ;  it  is  threaded  through  the 
sterilised  needle  as  far  as  its  middle.  The  two 
halves  of  the  waxed  silk  are  then  twisted  together 
into  a  single  cord.  Two  of  these  threaded  needles 
;ire  required.      The  part  of  the  suture  which  meets 


OPERATIONS  207 


with  the  greatest  resistance  in  passing  through 
the  tissues,  is  that  near  the  eye  of  the  needle. 
The  thread  must  be  double  here  in  any  case,  so 
one  may  as  well  have  the  benefit  of  the  double 
thickness  throughout.  The  wax-soaked  thread  is 
sufficiently  stiff,  at  the  ordinary  temperature  of  the 
air,  to  abstain  from  tying  itself  into  undesired 
knots  during  the  operation,  but  at  the  body  tem- 
perature it  is  quite  supple.  It  glides  easily  and 
with  a  minimum  of  damage  to  the  tissues— like 
a  well  greased  catheter.  It  is  practically  non- 
absorbent— an  important  point  in  a  region  which 
cannot  be  absolutely  aseptic. 

Anesthesia. —  For  young  children  a  general 
anaesthetic,  preferably  chloroform,  is  necessary. 
For  older  patients  a  local  anaesthetic  is  sufficient. 
I  use  the  crystals  of  hydrochlorate  of  cocaine, 
applied  twice  before  the  operation  at  intervals  of 
about  five  minutes.  During  general  anaesthesia 
the  eyes  usually  diverge,  so  that  one  has  to 
remember  the  angle  of  the  squint  and  produce 
approximately  the  effect  required.  Under  a  local 
anaesthetic  there  is  no  such  divergence,  so  that 
one  can  gauge  exactly  the  extent  to  which  the 
muscle  is  to  be  advanced.  For  this  reason,  I 
never  operate  under  general  anaesthesia  unless  I 
can  rely  upon  a  trained  fusion  faculty  to  do  the 
fine  adjustment. 

The   operation— -The   hands    of    the    surgeon 
and  nurses  are  sterilised.      The  patient's  face   is 


2o8  OPERATIONS 

thoroughly  cleansed.  The  conjunctival  sac  is 
irrigated  with  sterilised  saline  solution  (60  grains 
to  a  pint  of  water).  If  the  lacrymal  apparatus 
and  conjunctiva  are  not  perfectly  healthy,  the 
operation  is  postponed  until  they  are.  Just  after 
the  irrigation,  and  from  time  to  time  during  the 
operation,  a  few  drops  of  supra-renal  gland  extract 
are  instilled.  1  use  Parke  Davis  and  Co.'s  adre- 
nalin chloride  solution.  The  vascular  constriction 
caused  by  the  extract  makes  the  operation  blood- 
less or  nearly  so,  so  that  one  is  not  impeded  in 
one's  work  by  the  necessity  for  constant  sponging. 
The  patient  lies  on  the  table  in  a  good  light, 
with  his  feet  towards  the  window.  His  lids  are- 
held  open  by  the  speculum.  The  surgeon,  stand- 
ing behind  the  patient's  head,  grasps  the  con- 
junctiva with  the  toothed  forceps,  while,  with  the 
scissors,  he  makes  a  straight  vertical  incision 
through  it  about  half  an  inch  long.  The  middle 
of  the  incision  is  close  to  the  corneal  margin.  A 
similar  incision  is  then  made  through  the  capsule 
of  Tenon.  The  conjunctiva  and  capsule  then 
retract,  or,  if  necessary,  they  are  pushed  back,  so 
as  to  expose  the  insertion  of  the  tendon.  If  the 
angle  of  the  squint  is  of  high  degree,  the  vertical 
incision  through  the  membranes  is  made  curved 
instead  of  straight,  the  convexity  of  the  curve 
beim>"  towards  the  cornea.  This  is  to  allow  the 
membranes  to  retract  more  freely.  One  blade  of 
the  advancement  forceps  is  now  passed  under  the 


OPERATIONS 


:oq 


tendon,  after  the  manner  of  a  tenotomy  hook,  the 
other  blade  being  superficial  to  the  conjunctiva. 
The  forceps  is  now  closed,  so  that  tendon,  capsule 
of  Tenon,  and  conjunctiva  are  all  firmly  clamped 
together,  with  their  relations  undisturbed  except 
tor  the  retraction  of  the  membranes.  The  tendon, 
and  a  few  little  fibrous  bands  beneath  the  tendon, 
are  now  divided  with  scissors,  at  their  insertion 
into  the  sclerotic.  The  advancement  forceps, 
holding  the  tendon,  capsule,  and  conjunctiva,  can 
now  easily  be  lifted  up  so  as  to  get  a  good  view 
of  the  under  side  of  the  muscle. 

One  of  the  needles  is  then  passed  inwards  at 
A,  through  conjunctiva,  capsule,  and  muscle.  It  is 
then  again  passed  through  muscle,  capsule,  and 
conjunctiva,  and  brought  out  at  B.  The  bight 
of  the  thread  thus  encloses  about  the  lower  fourth 
of  the  width  of  the  muscle,  together  with  its  ten- 
dinous expansions  and  capsule  and  conjunctiva. 
The  other  needle  is  similarly  entered  at  A',  passed 
through  conjunctiva,  capsule,  and  muscle,  and 
brought  out  at  the  under  side  of  the  muscle.  It 
is  then  entered  again  at  the  under  side  of  the 
muscle  and  brought  out  through  the  conjunctiva 
at  B',  the  bight  of  this  suture  thus  enclosing 
the  upper  fourth  of  the  width  of  the  muscle,  &c. 
The  object  of  inserting  both  sutures,  before 
proceeding  further  with  either,  is  that  they  may 
be  symmetrically  placed.  The  ends  of  the 
thread  from  A'  and   B'  are  then  knotted  tightly 


2IO 


OPERATIONS 


at  C.  The  end  bearing  the  needle  is  then 
entered  at  D,  and  passed  through  conjunctiva, 
capsule,  and  muscle,  and  carried  beneath  the 
lower  blade  of  the  advancement  forceps  nearly  to 
the  corneal  margin.      The  needle  is  here  passed 


Fig.  37. 


through  the  tough  circumcorneal  fibrous  tissue, 
and  brought  out  at  G'.  The  two  ends  of  the 
thread  are  then  temporarily  tied  loosely,  with 
a^ single  hitch,  at  H.  The  first  suture  is  then 
similarly  completed.  The  anterior  part  of  the 
muscle    and    capsule    and    conjunctiva    are    then 


OPERATIONS  2  I  I 

removed,  by  cutting  them  through  with  scissors 
behind  where  they  are  grasped  by  the  advance- 
ment forceps.  The  gap  is  then  closed  by  tight- 
ening and  securely  tying  each  suture  at  HH,  so 
that  the  eyeball  is  rotated  in  its  correct  position, 
and  the  anterior  end  of  the  muscle  is  brought 
nearly  up  to  the  corneal  margin  at  GG'. 

In  operating  under  cocaine,  before  the  knots 
are  tied  at  HH,  an  assistant  holds  the  globe  in 
the  primary  position  with  forceps,  while  the 
patient  is  told  to  try  to  look  away  from  the 
operated  muscle.  This  relaxes  the  muscle  while 
it  is  being  drawn  forward  by  the  sutures.  The 
sutures  are  then  temporarily  secured  at  HH,  by 
the  first  hitch  of  "the  surgeon's  knot."  The 
assistant  then  releases  the  globe.  The  fine 
adjustment  is  done  by  tightening  or  loosening 
the  hitches  at  HH,  the  result  being  checked  by 
the  mirror  test  or  by  the  reflection  of  a  candle 
flame  on  the  corneae.  The  surgeon's  knots  at 
H  H   are  then  completed. 

The  longitudinal  position,  on  the  muscle,  of  the 
loops  ABC  and  A'  B'  C,  varies  approximately 
according  to  the  degree  of  rotation  required. 

In  operating  under  cocaine,  the  immediate 
effect  is  the  permanent  result.  No  over-correction, 
therefore,  is  necessary.  In  operating  under  general 
anaesthesia,  one  has  to  bear  in  mind  the  angle  of 
the  deviation  and  produce  approximately  that 
decree  of  rotation. 


2  I  2  OPERATIONS 

After  the  operation,  the  eye  is  irrigated  with 
sterilised  saline  solution,  a  little  boric  ointment 
smeared  on  the  edges  of  the  lids,  and  a  gauze  pad 
applied. 

After-treatment. — The  eye  is  irrigated  and 
dressed  every  day.  The  more  quiet  the  eye  is 
kept,  during  the  first  few  days,  the  more  quickly 
will  the  wound  heal.  I  prefer,  therefore,  to  keep 
the  patient  in  bed,  with  both  eyes  bandaged  for 
the  first  four  or  five  days.  After  this  time  his 
unoperated  eye  is  uncovered,  and  atropised  to 
prevent  any  effort  of  accommodation.  His  spec- 
tacles, if  he  has  any,  are  put  on  over  his  bandage. 
It  is  a  good  plan  to  stick  two  pieces  of  postage 
stamp  paper  on  the  lens  before  the  unoperated 
eye,  so  as  to  leave  a  narrow  vertical  slit  between 
them.  If  the  patient  looks  only  through  the  slit, 
he  can  look  up  or  down,  but  does  not  make  any 
horizontal  or  accommodative  movements,  which 
might  retard  the  healing  of  the  wound.  The 
stitches  are  removed  on  the  eighth  day.  The 
bandage  is  discarded  two  days  later. 

Musculo- capsular  advancement. — In  many  cases 
of  neuropathic  divergence,  and  in  some  old  cases 
of  divergence  following  tenotomy  of  an  internal 
rectus,  it  is  advisable  to  bring  forward  the  capsule 
of  Tenon  and  conjunctiva  as  well  as  the  enfeebled 
muscle.  These  membranes  have  little  elasticity, 
so  that  movement  in  the  opposite  direction  will 
be  restricted. 


OPERATIONS 


213 


Seize  the  conjunctiva  and  capsule  of  Tenon  just 
above  or  below  the  insertion  of  the  muscle  to  be 
advanced.  Snip  through  these  membranes  with 
scissors.  Introduce  one  blade  of  an  advancement 
forceps,  and  hook  this  blade  under  the  tendon, 
after  the  manner  of  a  tenotomy  hook.  Close  the 
forceps.  The  membranes  and  tendon  are  thus 
clamped  together,  so  that  no  retraction  of  the 
former  is  permitted.  Now  make  the  long  vertical 
incision  near  the  corneal  margin,  and  proceed 
with  the  advancement  as  already  described. 

Secondary  advancement.  — Not  infrequently  a 
patient  presents  himself  with  one  eye  widely 
divergent  as  a  result  of  tenotomy  of  an  internal 
rectus  muscle.  Usually,  an  excellent  cosmetic 
result  may  be  obtained  by  advancing  the  retracted 
muscle,  even  after  many  years.  Sometimes,  how- 
ever, the  muscle  is  much  atrophied  from  disuse. 

The  conjunctiva  and  capsule  of  Tenon  will  be 
matted  to  the  globe  in  the  neighbourhood  of  the 
former  insertion  of  the  muscle,  or  the  eyeball  may 
be  quite  destitute  of  covering  in  this  region. 
Grasp  the  membranes,  with  toothed  forceps,  well 
above  or  below  the  scarred  area,  and,  with  the 
scissors,  separate  them  from  the  nasal  side  of  the 
eye.  A  squint  hook  may  be  of  assistance  in  this. 
If  the  muscle  is  not  found  attached  to  some 
portion  of  the  anterior  segment  of  the  globe  it 
is  of  no  use  searching  for  it  with  a  squint  hook  far 
back.  It  is  never  found  attached  to  the  posterior 
15 


214  OPERATIONS 

hemisphere.  Seize  the  coverings  of  the  eye  in 
the  region  of  the  sunken  caruncle,  pull  them 
forward,  lift  them  up.  The  muscle,  or  what 
remains  of  it,  will  be  seen  on  their  under  surface. 
I  think  that,  after  tenotomy,  the  tendon  fails  to 
become  reattached  directly  to  the  globe  far  more 
often  than  is  generally  supposed.  If  the  muscle 
be  fairly  good  it  may  be  advanced  in  the  ordinary 
way.  If,  however,  it  be  much  atrophied,  a  musculo- 
capsular  advancement  is  preferable.  The  muscle 
and  membranes  are  seized  with  toothed  forceps 
and  drawn  between  the  jaws  of  an  advancement 
forceps.  The  surface  to  which  the  muscle  and 
membranes  are  to  be  attached  must  be  well 
refreshed. 

Tenotomy. 

There  are  several  slightly  different  methods  of 
performing  this  little  operation.  The  following  is 
as  good  as  any  other.  The  instruments  required 
are  speculum  (fig.  29),  straight  blunt-pointed 
scissors  (fig.  34),  tenotomy  hook  (fig.  35),  and 
fixation  forceps  (fig.  36).  The  patient  lies  on  a 
table.  Both  eyes  are  cocainised.  The  eye  to  be 
operated  upon  is  irrigated  with  sterilised  saline 
solution,  and  a  drop  of  supra-renal  extract  is 
instilled.  In  operating  on  the  left  internal  rectus, 
it  is  more  convenient  to  stand  in  front,  and  on  the 
left  of  the  patient.  In  tenotomising  any  of  the 
other  recti,  I  prefer  to  stand  behind  the  patient's 
head.     The  speculum  is  inserted,  if  the  muscle  to 


OPERATIONS  2  15 

be  tenotomised  be  one  of  the  external  or  internal 
recti.  In  the  case  of  a  superior  or  inferior  rectus, 
the  lids  should  be  held  open  by  the  fingers  of  an 
assistant.  Tell  the  patient  to  look  in  a  direction 
opposite  to  that  of  the  tendon  to  be  divided,  so  as 
to  bring  its  insertion  well  forward.  With  the  for- 
ceps, pick  up  the  conjunctiva  over  the  insertion  of 
the  tendon,  and,  with  the  scissors,  make  an  incision, 
about  one-third  of  an  inch  long,  in  a  direction  at 
right  angles  to  that  of  the  tendon.  Now  divide 
the  capsule  of  Tenon  in  the  same  way.  This 
brings  the  insertion  of  the  tendon  into  view. 
While  the  forceps  still  hold  up  the  cut  edge  of  the 
capsule,  make  a  few  short  snips  with  the  scissors 
near  one  border  of  the  tendon,  until  the  point  of 
the  scissors  is  felt  to  slip  freely  back  without 
encountering  any  resistance.  Now  lay  down  the 
scissors,  and  take  up  the  hook  in  the  right  hand. 
Pass  the  point  of  the  hook  into  this  incision,  and 
hook  it  round  the  insertion  of  the  tendon,  until 
it  appears  at  the  other  border.  During  this 
manoeuvre,  the  point  of  the  hook  should  be  kept 
in  contact  with  the  sclerotic.  Now  lay  down  the 
forceps,  and  transfer  the  hook  to  the  left  hand. 
Take  care  to  avoid  any  dragging  with  the  hook, 
as  this  causes  pain.  With  the  scissors,  cut 
between  the  point  of  the  hook  and  the  globe, 
until  the  tendon  is  divided  at  its  insertion,  and 
the  hook  comes  away.  It  is  usual  to  reintroduce 
the  hook,  to  seek  for  any  fibres  of  insertion  which 


2l6  OPERATIONS 

may  have  escaped  division.  It  is  not  necessary 
or  advisable  to  suture  the  conjunctiva,  unless  the 
conjunctival  incision  is  unusually  large. 

After  the  operation,  there  is  a  very  considerable 
defect  of  movement  in  the  direction  of  action  of 
the  tenotomised  muscle.  This,  to  some  extent, 
subsequently  disappears.  The  average  effect  of  a 
tenotomy  of  the  internal  rectus  is  130,  and  of  the 
other  recti  less  than  half  this  amount.  But  it 
varies  within  extremely  wide  limits. 

A  pad  and  bandage  should  be  worn  for  the  first 
forty-eight  hours,  after  which  it  may  be  discarded. 
The  eye  should  be  bathed  with  boric  lotion,  three 
or  four  times  a  day,  until  the  wound  is  healed. 

Complete  central  tenotomy . —  In  America,  partial 
tenotomies  are  very  commonly  performed.  I 
believe  these  to  be  useless,  as,  until  the  whole  of 
the  tendon  proper  has  been  divided,  no  appre- 
ciable effect  is  produced.  But  the  neat  and 
precise  method  by  which  these  partial  tenotomies 
are  performed  is  very  well  worth  copying.  By 
this  method,  the  tendon  itself  may  be  completely 
divided,  leaving  its  lateral  expansions  absolutely 
intact. 

The  patient  is  prepared  as  for  an  ordinary  teno- 
tomy. The  forceps,  scissors,  and  tenotomy  hook 
required  are  those  of  Stevens  (figs.  40,  3$,  and  39). 
The  surgeon,  standing  behind  the  patient's  head, 
seizes,  with  the  forceps,  the  conjunctiva  over  the 
tendon  near  its  insertion.       A   transverse  incision 


OPERATIONS 


217 


of  sufficient  length  is  made  through  the  con- 
junctiva. The  capsule  of  Tenon  is  now  similarly 
incised,  to  an  extent  just  sufficient  to  expose  the 


tendon.  The  central  fibres  of  the  tendon  are 
next  grasped  by  the  forceps,  and  a  button-hole  is 
snipped  through  the  tendon  with  the  scissors. 
The  forceps  being  laid  aside,  the  small  tenotomy 


2l8  OPERATIONS 

hook  is  introduced  through  this  button-hole,  with 
its  point  turned  towards  one  border  of  the  tendon, 
Half  the  tendon  is  cautiously  snipped  through  on 
the  hook,  from  the  centre  towards  the  edge.  The 
point  of  the  hook  is  now  turned  round,  and  the 
other  half  of  the  tendon  similarly  divided. 

When  the  hook  is  first  introduced  through  the 
button-hole,  on  lifting  it  up,  the  tension  of  the 
tendon  is  felt.  When  the  whole  of  the  tendon 
proper  has  been  divided,  considerable  tension  is 
still  felt,  by  means  of  the  hook,  at  the  edges 
of  the  wound.  This  resistance  is  due  to  the 
lateral  expansions  of  the  tendon.  These  should 
on  no  account  be  divided,  as  it  is  upon  the  pre- 
servation of  these  lateral  expansions  that  the 
safety  of  this  operation  depends.  Sometimes  it 
is  impossible  to  define  exactly  the  edge  of  the 
tendon,  owing  to  its  gradually  merging  into  its 
lateral  expansions.  In  such  a  case,  one  has  to  be 
guided  by  the  degree  of  tension  felt  by  the  hook. 

No  after-treatment  is  required  beyond  frequent 
bathing  with  boric  lotion  or  sterilised  saline 
solution. 

This  operation  appears  to  be  a  safe  one  when 
judiciously  employed,  but  the  effect  produced  by 
it  is  small— about  6°  or  y°  in  the  case  of  the 
internal  rectus,  and  30  in  the  case  of  the  superior 
rectus.  It  varies  very  little  in  different  cases,  and 
shows  no  tendency  to  increase  with  time.  I  have 
usually  seen  a  slight  decrease  after  a  few  weeks. 


219 


APPENDIX. 


Congenital  Amblyopia. 

Table  VI.  shows  the  degrees  of  refractive  error  and 
the  visual  acuity  in  the  twenty-three  cases  of  congenital 
amblyopia  described  in  Chapter  V. 


Table  VI. 


Better  Eve. 

Worse  Eye. 

Refractive  error. 

Vision. 

Refractive  error. 

Vision. 

Lower 

Higher 

Lower 

Higher 

meridian. 

meridian. 

meridian. 

meridian. 

+  1 

+  1 

t 

+  2-5 

+  4 

A 

—  0-5 

O 

| 

-0-5 

+  4-5 

A 

+  T5 

+  i-5 

§ 

+  1 

+  3-5 

ft 

—  i"5 

+  2 

s 

—  2 

+  2-5 

A 

+  2 

+  1 

6 

+  2 

+  5 

A 

+  2 

+  1-25 

1 

0 

+  5-25 

A 

+  L25 

+  1-25 

§ 

+  5 

+  7 

A 

+  i-5 

+  i-5 

1 

+  5 

+  6-5 

A 

+  4 

+  4 

I 

+  5-5 

+  8-5 

* 

+  o-5 

+  0-5 

f 

+  1 

+  1 

35 

+  o-5 

+  0-5 

6 

+  4 

+  6 

A 

+  i 

+  1-25 

f 

+  1 

+  4-5 

A 

+  3-5 

+  3'5 

| 

+  2 

+  6-5 

A 

+  i-5 

+  175 

§ 

+  i-5 

+  475 

A 

+  o-5 

+  0-5 

6_ 

—  1 

+  3 

A 

+  i 

+  1 

| 

+  1 

+  4 

ft 

o 

0 

f 

+  4 

+  6-5 

ft 

+  3 

+  3-5 

6 

+  3 

+  7 

A 

+  i 

+  1 

8 

—  i'5 

+  2-5 

ft 

+  075 

+  1 

9 

+  3 

+  5-5 

A 

+  2 

+  2 

6 
5 

+  2 

+  6-5 

A 

+  0-5 

+  0-5 

9 

+  1 

+  4-5 

A 

+  0-25 

+  075 

I 

+  T5 

+  5-5 

ft 

220 


APPENDIX 


Table  VII.  shows  the  refractive  error  and  the  visual 
acuity  of  the  eleven  cases  in  Table  III.,  Chapter  V., 
which  had  an  amblyopia  of  T6«  or  higher.  The  visual 
defect  in  these  cases  also  is  almost  certainly  congenital. 


Table  VII. 


Fixing  Eye. 

Deviating  Eye. 

Refractive  error. 

Vision. 

Refractive  error. 

Lower 

Higher 

Higher 

Lower 

Vision. 

Meridian. 

Meridian. 

Meridian. 

Meridian. 

+  2 

+  2 

| 

+  i-5 

+  5-5 

A 

+  3"5 

+  4 

5 

+  3-5 

+  6 

A 

+  i-5 

+  i-5 

§ 

+  i-5 

+  5 

A 

+  4 

+  4'5 

1 

+  2 

+  5-25 

& 

+  2 

+  3 

S 

+  2 

+  7 

& 

+  1 

+  1 

I 

+  1 

+  3-5 

A 

+  2-5 

+  3 

? 

+  0-5 

+  J5 

A 

+  3 

+  3 

I 

+  3-5 

+  7'5 

A 

+  0-5 

+  0-5 

f 

—  1 

+  275 

A 

+  275 

+  3-5 

g 

+  1 

+  5"5 

A 

+  1-25 

+  1-25 

6 

+  4-5 

+  8-5 

A 

Prisms  and  Decentred  Lenses. 

There  are  several  systems  of  numbering  prisms.  In 
ordering  a  prism  it  is  necessary,  therefore,  to  specify 
which  system  one  uses.  In  this  book  the  strength  of 
a  prism  is  expressed  by  the  number  of  degrees  which 
it  deflects  a  ray  of  light.  This  "  deviating  power  "  is 
about  half  the  geometrical  angle  (the  angle  between 
the  two  plane  surfaces). 

A  prism  causes  mal-projection,  and  chromatic  dis- 
persion of  white  light.  Clinically,  mal-projection  is 
avoided  by  dividing  the  prism  between  the  two  eyes. 
For  instance,  in  a  case  of  right  hyperphoria  20,  if  one 
wished  to  correct  l£°  of  the  error,  one  would  order  a 
prism  :,!°  apex  up,  before  the  right  eye,  and  a  prism 
of  the  same  strength,  apex  down,  before  the  left  eye. 


APPENDIX 


221 


Chromatic  dispersion  is  not  noticeable  in  a  prism  which 
does  not  exceed  2°  deviating  power. 

A  pencil  of  parallel  rays  which  traverses  a  spherical 
lens  at  its  optical  centre,  is  made  convergent  or  diver- 
gent. A  pencil  of  rays,  traversing  a  lens  towards  its 
periphery,  is  deflected  in  addition  (as  by  a  prism) 
towards  the  axis  of  a  convex  lens  away  from  the  axis 
of  a  concave  lens. 

Glasses  containing  prisms  in  combination  with 
spherical  and  cylindrical  lenses  are  expensive,  because 
they  must  be  specially  ground — the  optician  cannot 
prepare  them  from  his  stock.  But  if  the  patient  has 
to  wear  fairly  strong  lenses,  and  if  the  required  pris- 
matic effect  is  small,  this  may  be  secured  by  decentring 
the  spectacle  glass.  That  is,  the  optician,  instead  of 
cutting  the  spectacle  glass  from  the  middle  of  one  of 
his  ready-ground  lenses,  cuts  it  from  one  side.  This 
is  much  cheaper.  The  effect  of  decentring  a  cylin- 
drical lens,  in  a  direction  at  right  angles  to  its  axis, 
is  the  same  as  that  of  decentring  a  spherical  lens.  In 
a  lens  of  the  ordinary  stock  size,  there  is  room  to 
decentre  a  medium-sized  spectacle  glass  about  3  mm., 
i.e.,  a  total  of  6  mm.  in  the  two  eyes. 

The  following  table,  prepared  from  Dr.  Maddox's 
formula,  shows  the  prismatic  effect  of  decentring 
lenses. 


2  mm. 

3  mm. 

4  mm. 

5  mm. 

6  mm. 

2  D. 

14' 

21' 

27' 

35' 

41' 

3  D. 

2l' 

31' 

41' 

52' 

1°  2 

4  D. 

27' 

41' 

55' 

i°  10 

1°  22' 

5  D. 

35' 

52' 

i°  10' 

i°  26' 

i°43' 

6  D. 

4i' 

1°  2' 

i°  22' 

i°43' 

2°  4' 

7  D- 

48' 

1°  12' 

i°36' 

2° 

2°  24' 

8  D 

55' 

1°  22' 

i°5° 

2°  I9' 

20  45' 

222  appendix 

Results  of  Fusion  Training. 

In  the  earlier  cases  I  had  not  perfected  my  methods 
of  fusion  training,  and  in  recent  cases  sufficient  time 
has  not  yet  elapsed  to  show  that  the  results  are  per- 
manent. I  therefore  give  the  results  of  fusion  training 
in  ioo  consecutive  cases,  beginning  January,  1896. 
Five  were  what  1  have  called  essentially  alternating 
squints,  in  which  I  was  unable  to  get  even  simulta- 
neous vision  of  the  two  object  slides.  In  17  cases  the 
patients  were  more  than  6  years  of  age.  I  got  a 
moderately  good  result  in  two  of  these,  and  failed  in 
the  other  15.  I  scarcely  ever  now  attempt  fusion 
training  after  6  years  of  age.  Of  the  remaining  78 
cases,  which  alone  were  suitable  for  fusion  training, 
I  failed  in  12  cases  (owing  to  intractability  of  patient, 
irregularity  of  attendance,  or  apparent  absence  of  the 
power  acquiring  fusion)  ;  in  seven  cases  the  result  was 
only  moderate,  and  in  59  cases  a  good  amplitude  of 
fusion  was  developed.  In  two  of  these  cases  the 
parents  refused  advancement  which  was  necessary  to 
complete  the  cure  ;  four  cases  have  been  lost  sight  of ; 
the  remaining  53  cases  are  perfectly  and  permanently 
cured. 

Results  of  Advancement  Operations. 

In  performing  advancement  I  have,  since  1898, 
relied  exclusively  upon  the  method  described  in  Chap- 
ter XII.  I  therefore  give  results  of  100  consecutive 
advancement  operations,  beginning  January,  1899.  I 
have  re-examined  most  of  these  cases  within  the 
present  year  (1906). 

By  primary  advancement  I  mean  advancement  of 
a  muscle  which  had  not  previously  been  operated 
upon.  In  some  of  these  cases  the  opposing  muscle 
had  previously  been  tenotomised  by  some  other  sur- 
geon.    By  secondary   advancement    I    mean  operation 


APPENDIX 


223 


upon  a  muscle  which  had  previously  been  tenotomised 
or  unsuccessfully  advanced. 

In  cases  in  which  the  fusion  sense  has  been  fairly 
well  developed,  but  in  which  the  deviation  persists, 
the  object  of  operation  is  to  put  the  eyes  into  such 
a  position  that  the  patient  will  have  binocular  single 
vision.  If  the  fusion  sense  cannot  be  developed,  one 
aims  at  removing  the  visible  deformity.  Cases  which 
come  up  to  this  standard  I  have  classified  as  success- 
ful. Those  which  do  not  I  have  called  unsuccessful, 
although  in  all  these  cases  there  was  considerable 
improvement. 

Eighty-six  operations  were  performed  under  cocaine 
and  14  under  chloroform. 

The  100  cases  consisted  of  : — 


Secondary 


The  77  cases  of  primary  advancement  of  external 
rectus  included  one  case  of  congenital  paralysis  of 
external  rectus  and  two  cases  in  which  the  muscle 
was  atrophied.  In  these  three  cases,  though  a  per- 
fect result  was  not  to  be  expected,  musculo-capsular 
advancement,  combined  with  tenotomy  of  the  oppos- 
ing muscle,  produced  considerable  improvement  in 
the  appearance. 

Of  the  74  remaining  primary  advancements  of 
external  rectus,  66  were  successful  ;  in  three  other 
cases  a  second  operation1  proved  successful  ;  in  one  a 
second  operation  was  recommended  but  was  refused ; 
in  four  cases,  though  the  results  did  not  satisfy  me, 


1  I  have  not  included  these  three  cases  in  the  list  of  secondary 
advancements  recorded  below. 


external 

rectus 

...       77 

internal 

„ 

8 

inferior 

„ 

1 

external 

„ 

4 

internal 

„ 

9 

superior 

„ 

1 

224  APPENDIX 

the  patients  were  quite  satisfied,  so,  as  there  was  no 
fusion  sense  in  any  of  these  four  cases,  I  did  not  urge 
further  operation.  In  17  of  these  74  cases  the  internal 
rectus  was  tenotomised  at  the  same  time. 

Of  the  eight  primary  advancements  of  internal 
rectus,  two  were  old  myopic  divergent  squints,  and 
two  were  neuropathic  divergent  squints  with  some 
fusion  sense.  These  were  successful.  The  remaining 
four  were  neuropathic  divergent  squints  with  no 
fusion  sense.  Considerable  improvement  in  appear- 
ance was  produced  in  these  four  cases,  but  the  results 
were  far  from  perfect  (see  p.  138).  The  external  rectus 
was  not  tenotomised  in  any  case. 

The  primary  advancement  of  inferior  rectus  was 
in  a  case  of  vertical  deviation  of  high  degree  with 
absence  of  fusion  sense.  I  succeeded  in  removing 
the  deformity. 

The  four  secondary  advancements  of  external  rectus 
were  in  cases  in  which  some  one  had  unsuccessfully 
attempted  advancement.  In  one  case  I  succeeded. 
In  the  other  three  the  previous  mutilation1  of  the  parts 
rendered  a  perfect  result  impossible. 

The  nine  secondary  advancements  of  the  internal 
rectus  were  all  cases  in  which  tenotomy  of  this  muscle 
had  been  followed  by  divergence  of  the  eye.  I  was 
responsible  for  two  of  these  tenotomies.  Five  of  these 
secondary  advancements  were  successful  ;  in  three 
the  condition  was  improved  ;  in  one  there  was  no 
improvement. 

The  secondary  advancement  of  the  superior  rectus 
has  already  been  described  (Case  D,  227,  p.  153). 

1  If  a  suture  lias  been  tied  on  the  muscle,  including  its  whole 
width,  the  muscle  in  front  of  the  ligature  atrophies  just  as  surely 
as  if  it  had  been  cut  off  with  scissors. 

If  a  surgeon  in  advancing  a  muscle  has  isolated  it  from  its 
overlyin-  membranes  and  its  Literal  expansions,  if  one  has  to 
operate  again  upon  this  muscle  one  finds  a  shapeless  mat  of 
muscle  and  scar  tissue. 


APPENDIX 


225 


The  Deviometer  (p.  89). 

The  patient's  eye  is  only  two  feet  from  the  instru- 
ment. In  looking  at  the  button  above  the  light  he 
will,  therefore,  exercise  a  dynamic  convergence  pro- 
portionate to  that  distance.  It  has  often  been  sug- 
gested to  me  that  this  would  cause  the  degree  of  a 
convergent  squint  to  appear  greater  than  it  really  is. 
This  is  not  the  case,  because  the  surgeon's  eye  is  at 
the  same  distance,  just  above  the  zero  of  the  scale. 
This  is  easily  demonstrated  by  experiment  with  a 
normal-sighted  person.  When  he  looks  at  the  button 
both  visual  axes  converge  to  this  point.  The  surgeon 
places  his  eye  at  the  same  distance — just  above  the 
button — so  that  he  sees  the  vertical  lines  of  light 
occupying  symmetrical  positions  on  the  corneas  of 
the  observed  person,  showing  that  the  latter  has  no 
squint.  If  the  observed  person  could  look  at  the 
button  with  one  eye,  without  exercising  any  dynamic 
convergence  (keeping  his  visual  axes  parallel),  he 
would  appear  to  the  surgeon  to  have  a  divergent 
squint — in  fact,  he  would  have  a  divergent  squint  for 
that  distance. 

No  adjustments  are  required  except  that  the  60  cm. 
string  must  be  kept  taut.  As  the  scale  is  flat,  instead 
of  a  curved  arc,  a  slight  lateral  movement  on  the  part 
of  the  patient  introduces  no  appreciable  error.  The 
height  of  the  patient's  eyes  above  the  tables  makes  no 
difference. 

Details  of  construction.  The  woodwork  can  be  made 
by  any  carpenter  for  a  few  shillings.  The  following 
measurements  have  been  found  satisfactory  : — 

The  pedestal,  10  inches  wide,  5  inches  deep,  from 
before  backwards,  i\  inches  high. 

The  upright  board,  height  13  \  inches  (11  inches 
above  pedestal),  width  5  inches,  thickness  f  inch. 

The  arm  is  pivoted  at  one  end  by  a  bolt  which 
passes  through  the  upright  board.    There  is  a  chock  on 


226 


APPENDIX 


each  side,  on  one  of  which  it  rests.  It  is  swung  over 
to  either  side  as  required.  This  arm  is  of  hard  wood, 
27  inches  long,  2  inches  wide,  T\  inch  thick.  It  is 
painted  black  in  front.  A  long  strip  of  white  paper  or 
celluloid,  about  half  an  inch  wide,  has  marked  on  it  the 
tangents  to  degrees  at  the  distance  of  60  cm.  This 
strip  is  pasted  on  the  back  of  the  arm,  with  the  zero 
of  the  scale  at  the  pivot  hole. 

The  tangents  to  degrees  at  60  cm.  are — 


2*1  cm. 

4'2  „ 

6-3  „ 

8-4  „ 

io-6  „ 

12-8  „ 

15  » 

I7'2  „ 


18° 

20° 
■79° 

24°- 
26°- 

28°  • 

300 


19-5  cm. 

21-8  „ 

24-2  „ 

267  „ 

29-3  » 

319  >. 

■347  „ 

3TS  » 


340  — 40-5  cm. 

36°-43-6  „ 

380  — 46-9  „ 

400  — 50-3  „ 

420— 54  » 

44°— 57'9  ., 

460  —  62-6  „ 

480  — 667  „ 


In  inserting  the  bell  push  only  one  wire  is  cut, 
the  other  being  left  intact.  The  instrument  is  made 
by  Messrs.  Bonnella  and  Son,  58,  Mortimer  Street, 
London,  W. 


Modifications  of  the  Amblyoscopk. 

Dr.  ERNEST  Maddox  uses  a  quickly  acting  screw, 
instead  of  the  short  slot  in  the  brass  arc.  This  ad- 
mits of  delicate  adjustment,  which  is  an  advantage  in 
testing  the  horizontal  breadth  of  fusion. 

Dr.  Freeland  Fergus  employs  a  method  of  illumi- 
nating the  object  slides  which  is  certainly  more  compact 
than  the  apparatus  shown  in  fig.  12,  and  is  probably 
equally  efficacious.  "  Immediately  behind  the  parts  of 
the  Amblyoscope  into  which  the  pictures  arc  placed, 
there  is  a  stout  metal  collar  from  which  a  curved  piece 
of  metal  is  carried  in  front  of  the  pictures.  To  each 
of  the  two  pieces  of  metal  an  electric  lamp  of  about 
three-candle  power  is  attached.  From  each  of  the  two 
lamps  a  lead  is  taken  to  a  rheostat,  so  that  the  amount 
of  illumination  of  each  is  thoroughly  under  control." 


APPENDIX 


227 


Dr.  Maitland  Ramsay  has  substituted  total-re- 
flecting prisms  for  the  mirrors  ("  Ophthalmoscope," 
vol.  3).  These  are,  of  course,  very  perfect  reflectors, 
but  very  expensive.  He  has  also  devised  an  improved 
lighting  apparatus.  "  The  lighting  is  arranged  by 
means   of    two    small    lamps,    one   fixed    immediately 


Fig.  41. 


Fig.  42 


behind  each  picture  in  the  Amblyoscope.  The  degree 
of  illumination  is  varied  and  regulated  by  a  sliding 
bridge-resistance,  which  can  be  adjusted  most  delicately 
and  which,  while  it  takes  resistance  from  the  circuit  of 
one  lamp  and  so  increases  its  brightness,  at  the  same 
time  throws  more  resistance  into  that  of  the  other  and 
brings  about  corresponding  diminution  of  its  brilliancy. 


228 


APPENDIX 


The  illustrations  show  the  arrangement,  which  has 
been  carried  out  by  Mr.  Trotter,  40,  Gordon  Street, 
Glasgow." 

Dr.  Nelson  Miles  Black  has  added  a  vertical 
screw  adjustment,  by  means  of  which  one  tube  can  be 
moved  above  or  below  the  plane  of  the  other,  in  order 
more  readily  to  adapt  the  instrument  to  cases  of  squint 
in  which  there  is  a  vertical  deviation.  By  means  of 
this  ingenious  device,  one  may,  in  a  case  of  obstinate 
suppression,  call  attention  to  the  second  image  by 
temporarily  throwing  it  above  or  below  the  plane  of 
the  other. 

Advancement  Forceps. 

Messrs.  Weiss  and  Son  have  made  for  me  an 
advancement  forceps  on  the  Prince  model,  which 
seems  perfect.  There  are  no  spikes,  the  blades  are 
smooth    and   probe-pointed,  so    the  instrument  is  as 

KKSffllltar 


Fig.  43- 

easy  to  introduce  as  a  tenotomy  forceps.  The  catch 
gives  a  firm  grip  and  has  not  the  same  tendency  as 
the  spring  catch  to  get  out  of  order.  Only  one  forceps 
is  required. 


229 


INDEX 


Abduction 
Abversion ... 

,,         in  cases  of  coir 
Accommodation  ... 


ergent  squint 


PAGE 

.  180 
4 

27.49 
1 


and  convergence,  association  between 


Advancement 


,,  musculo-capsular 

secondary 
,,  results  of 

Ad  version ... 
Etiology  of  convergent  squint ... 

,,  ,,       author's  proposition  . 

.,  ,,  ,,       Donder's  theory 

,,  ,,  ,,       muscle  theory 

Amblyopia,  acquired  (amblyopia  ex  anopsia) ... 
,,  ,,         methods  of  curing 

„         method  of  preventing 

,,  congenital 

„  in  cases  of  convergent  squint 

Amblyoscope 

as  a  test  for  binocular  vision 
,,  illuminating  apparatus  for 

,,  object- slides  for    ... 

Angle  gamma       

„  ,,       method  of  measuring     ... 

Angle  of  deviation,  methods  of  measuring 

Anisometropia      

,,  in  convergent  squint 

„  predisposing  to  squint  . . . 


3 

201 

212 

140,213 

...     222 

4 

48 

54 

50 

...       48 

66,  77 

103,  105 

...     105 

63,  76,  219 

34,  76,  220 

120 

16 

122 

123 

5 

94 


Astigmatism 


i6 


in  convergent  squint 

in  congenitally  amblyopic  eyes 


65: 


5 
47 
57 

5 
45 
220 


230  INDEX 

PAGE 

Atropine,  effect  of  ...  ...  ...  ...  ...         2 

„         instilled  into  fixing  eye  only  .. .  ...  ...      105 

,,         long-continued  use  of,  for  both  eyes  causes 
extreme  amblyopia  in  the  deviating  eye  70,  109,  154 

Binocular  vision           ...  ...  ...  ...  7,  86 

,,               ,,       grades  of  ...  ...  ...  ...  12 

.ry    .,,                ,,       in  infancy  ...  ...  ...  ...  20 

,,                ,,       tests  for  ...  ...  ...  ...  14 


21 

3 

3 

196 

198 


84 

3 

25 

30 

48 

46,  47,  61,  116 

...       27 

27,  28,  84 

30,61 

...       60 


Conjugate  movements  of  the  eyes  in  infancy  .. 
Convergence  and  accommodation,  association  between 
,,  dynamic    ... 

,,  dynamic,  insufficiency  of 

,,  dynamic,  method  of  investigatin 

,,  dynamic,  method  of  investigating  in  a 

case  of  squint  ... 
Convergence,  static 
Convergent  squint 

accidentally  alternating 
aetiology  of  ... 
alternating    ...        30,  42 
conjugate  movements  in 
dynamic  convergence  in 
essentially  alternating 
hereditary  influence  in 
measurement     of      the 
deviation 
Convergent  squint,  method  of  investigating  a  case  of 
,,  ,,       method  of  investigating  fixation  of 

deviating  eye  ... 
Convergent  squint,  unilateral  ... 

unilateral,  course  of  an  untreated 

case        ...          ...         ...         ...         ...         

Convergent  squint,  occasional  ... 


angle     of 


88 

78 

82 
29 

40 
116 


power  of  rotation  of  each  eye     27,  49,  83 
,,  ,,     spontaneous  "  cure "  of      ...         ...       39 

,,     statistical     tables    showing    visual 
acuity  of  deviating  eyes         ...  ...  ...  76-77 

Convergent    squint,  statistics  showing  age  at  which 
the  deviation  appears ...  ...  ...  ...  ...       42 


INDEX 


231 

PAGE 


Convergent     squint,     statistics     showing     refractive 

error  in ...          ...          ...          ...          ...  43 

Convergent  squint,  the  question  of  operation  in         ...  in 

ii               ,,       treatment  of           ...          ...         ...  97 

Cover  test  for  squint       ...          79 

Cyclophoria          166,  et  seq.,  188 

,,         experiments  to  explain  the  effect  of         ...  189 

Decentration  of  lenses        ...         ...     220 

Deviation,  methods  of  measuring  angle  of      ...  ...       88 

Deviometer           ...          ...          ...          ...          ...  89,  225 

Diplopia  artificially  produced 32,  87 

,,         in  convergent  squint  ...         ...         ...  32, 33 

,,         monocular        ...          ...          ...          ...  ...       36 

,,         physiological ...          ...  ...         9 

Divergence  in  extreme  myopia...          ...          ...  ...     138 

,,          of  blind  eyes           ...          ...      139 

,,          secondary  to  tenotomy       ...          ...  154,  139 

Divergent  squint,  infantile  myopic       ...         ...  ...     136 

,,             .»        myopic          .  .          ...          ...  ...      133 

,,             ,,        neuropathic...         ...         ...  ...      136 

Dynamic  convergence  (see  "  Convergence,  Dynamic  ") 
,,         refraction  (see  "  Refraction,  Dynamic  ") 

Emmetropia         ...         ...         ...         ...         1 

Esophoria...  ...  ...  166,  et  seq.,  183 

,,         mistaken  for  occasional  convergent  squint 

29,  183,  194 
Examination  of  a  case  of  convergent  squint  ...  ...       78 

Exophoria  ...  ...  ...  ...  166,  et  seq.,  185 

False  macula     ...         36 

Fevers,    specific,    preceding    the  appearance    of    a 

deviation           ...  ...          ...          ...       58 

Fixation     ...         ...         ...         ...  ...         ...         ...         3 

,,         false      ...  ...         ...         ...       36 

,,         in  deviating  eyes         ...  ...          ...       35,  76,  77 

,,         in  infancy         ...          ...  ...          ...          ...       20 

lost         36,  77 

,,         method  of  investigating  ...         ...         ...       84 

Four-dot  test        ..,         ...         ,..         ,. 15 


232 


INDEX 


Fusion,  amplitude  of       

,,       experiments  showing  elasticity  of 

,,       (see  also  "  Binocular  Vision  ") 

,,       sense,  defect  of,  the    fundamental    cause   of 


PAGE 

13.  129 
10,  11 


squint    ... 
Fusion  sense,  method  of  training 

,,  ,,      normal  development  of,  in  infancy 

,,      training,  results  of 

"Growing  out  of  a  Squint" 

Hereditary  influence  in  convergent  squint 

Hering's  drop  test 

Heterophoria 

Heterotropia        ...         

Hypermetropia    ... 

,,  causing    a    tendency 

squint     

Hypermetropia  in  convergent  squint 
Hyperphoria 


55>  60 

.     118 

20 

.     222 

•        39 

60 

17 

164 

.     168 


to    convergent 

50,56 

43 

166,  et  seq.,  186 


Infancy,  central  fixation  in ...         ...  20 

,,         conjugate  movements  of  the  eyes  in           ...  20 

,,         development  of  binocular  vision  in  ...          ...  20 

Infants,  spectacles  for  ...           ...          ...          ...         ioi,  102 

spurious  squint  of         ...          ...          ...           ..  38 

Insufficiency  of  dynamic  convergence...          ...          ...  196 

Investigation  of  a  case  of  convergent  squint  ...         ...  78 

Ivory-ball  test      85 

Lenses,  decentration  of        ...         ...         ...         ...  220 

Macula,  false    ...         ...         ...         ...          ...         ...  36 

Maddox  double  prism     ...         ...         ...         ...         ...  172 

,,        rod          170 

,,        tangent  scale 91,  172 

Mirror  test  for  convergent  squint ...         ...  80 

Muscular  balance  of  the  eyes,  methods  of  investigating  169 

Myopia 5»  43 

Myopic  divergent  squint             ...          ...          ...          ...  133 


Neuropathic  divergent  squint 


1 36 


INDEX  233 

PAGE 

Occlusion  of  fixing  eye        ...         ...     103 

Operation  in  cases  of  convergent  squint 

in,  144,  145,  148,  157,  159 

Operations  on  the  external  ocular  muscles     201 

Optical  correction  in  cases  of  convergent  squint        ...       98 
Orthophoria          I°4 

Paralysis  of  external  rectus  muscle     ...      33,  59,  81 

Perimeter  method  of  measuring  deviations 93 

Peripheral  form  vision,  method  of  testing       ...  ...       64 

Perspective,  sense  of      13,  I7>  I3° 

Phorometer  ..  ...  ...  ...  181 

Physiological  diplopia 9 

Presbyopia  ...  ...  ...  •■•  •••  •••         2 

Prism  duction      179 

Prisms  and  decentred  lenses     ...  ...  ...  •••     220 

Pseudo-heterophoria       ...  ...  ...  166 

Refraction,  dynamic    ...         ...         •••         2 

,,  investigation  of    ...  ...  ...  •••       95 

,,  static         ...         ...  ...  •••         •••  ! 

Refractive  error,  correction  of,  in  convergent  squint         98 
,,  ,,  „  in  divergent  squint    ..      135 

,,  ,,  ,,  in  heterophoria         ...     166 

,,  ,,  ,,  in  infants       ...  98.  102,  151 

,,  ,,     in  cases  of  convergent  squint  ...       43 

,,  ,,  ,,  divergent  squint  133,  137 

Results  of  advancement  operations      222 

,,        ,,  fusion  training  ...  ••     222 

Simultaneous  macular  perception             ...           13,  128 

Smith,  tape  method  of  Priestley           92 

Spurious  squint  of  infants          ...          ...          ...          •••  3& 

Squint,  convergent  (see  "Convergent  Squint") 
Squint,  divergent  (see  "  Divergent  Squint  ") 

or  paralysis,  differential  diagnosis      ...          ...  81 

,,       relative  frequency  of     ...          ...          ...          •••  47 

Static  convergence          ...          ...          ...          3 

,,      refraction  ...         ...         ...         ...         •••         •••  r 

Subduction           180 

Subversion            ...          ...          ...          •••  3 

Superduction        ,,,         ;rr         ...         ,,,         ,,,         ••»  J  80 


234  INDEX 

PAGE 

Superversion        ...          ...          ...          ...          ...  ...         3 

Suppression  of  the  vision  of  the  squinting  eye  ...       31 

Tangent  scale  of  Maddox    ...         ...         ...  91,  172 

Tenotomy...          ...          ...          ...          ...          ...  111,  214 

,,         complete  central        ...          ...          ...  ...     216 

,,         divergence  caused  by            ...             139,  154,  213 

Vertical  deviation,  apparent          ...         ...  ...       37 

,,                  ,,             true        ...          ...          ...  ...       38 

Vision,  binocular  (see  "  Binocular  Vision  ") 

Visual  acuity,  method  of  investigating            ...  ...       85 

of  deviating  eyes           ...          ...  ...76,77 

,,         ,,        peripheral,  method  of  investigating  ...       64 

Visual  axis  3 


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